CN109102815B - Encoding device and method, transcoding method and transcoder, and non-transitory medium - Google Patents

Abstract

The application discloses an encoding device and method, a transcoding method, a transcoder and a non-transitory medium. The coding method comprises the following steps: encoding a current content frame; generating a protection field for an associated metadata frame associated with the current content frame; encoding an associated metadata frame, including a protection field; and including the current content frame and the associated metadata frame in an output bitstream, wherein: generating the protection field involves generating one or more encrypted values; at least one of the one or more encryption values is a frame encryption value representing the authenticity of the current content frame; and generating a frame encryption value by applying a one-way function to a set of frames including the current content frame and the associated metadata frame.

Description

Encoding device and method, transcoding method and transcoder, non-transitory medium

This invention application is a divisional application of the invention patent application No. 201480005287.5, titled "Metadata Transcoding", which was filed on January 15, 2014 and entered the Chinese national phase on July 17, 2015.

Cross-references to related applications

This application claims priority from U.S. Provisional Patent Application No. 61/754,893, filed on January 21, 2013, the entire contents of which are incorporated herein by reference.

Technical field

This document deals with transcoding metadata. In particular, this document relates to methods and systems for transcoding metadata with reduced computational complexity.

Background technique

Currently, various single-channel and/or multi-channel audio rendering systems are used such as 5.1 multi-channel audio rendering systems, 7.1 multi-channel audio rendering systems or 9.1 multi-channel audio rendering systems. The audio rendering system enables, for example, the generation of surround sound originating from 5+1 speaker positions, 7+1 speaker positions or 9+1 speaker positions respectively. For efficient transmission or for efficient storage of corresponding single-channel audio signals or multi-channel audio signals, audio codec (encoder/decoder) systems such as Dolby Digital (DD) or Dolby Digital Plus (DD+) are used.

There may be a significant installed base of audio rendering devices configured to decode encoded audio signals using a specific audio codec system (eg, Dolby Digital). This particular audio codec system may for example be called a second audio codec. On the other hand, the evolution of the audio codec system may result in a newer audio codec system (eg, Dolby Digital Plus), which may, for example, be referred to as a first audio codec system. Newer audio codec systems may provide additional features (eg, increased number of channels) and/or improved encoding quality. In this way, content providers can tend to serve their content according to newer audio codec systems.

Nonetheless, users with audio rendering devices that employ decoders of the second audio codec system should still be able to render audio content that has been encoded according to the first audio codec system. This may be achieved by a so-called transcoder or converter configured to convert audio content encoded according to a first audio codec system into a second audio codec system. Encoded modified audio content.

Along the distribution chain of audio content, additional needs for transcoding may arise. Content providers can encode audio content using audio codecs that are well suited for the production and broadcast of audio content, such as the Dolby E audio codec. Audio content can be distributed using this production-oriented audio codec and can be modified based on a second audio codec such as a lossless codec such as Dolby TrueHD or a codec such as Dolby Digital Plus or Dolby Digital Transcode.

Typically, audio content is associated with metadata representing the audio content encoded in the bitstream. Typically, the audio content is separated into a sequence of frames, where each frame of the audio content includes a predetermined number of samples (eg, 1024 samples). Frames in the sequence of frames may be associated with corresponding metadata containers or metadata frames. A metadata container may represent information describing frames of audio content associated with the container. An example of such information describing a frame may be loudness data about some or all samples of the frame. Alternatively or additionally, a metadata container may be used to transport auxiliary data that may not be directly associated with the corresponding frame of audio content. Such auxiliary data may be used, for example, to provide a decoder of an audio codec system with a firmware upgrade.

In addition to transcoding audio content from a first audio codec system to a second audio codec system, the transcoder typically also needs to transcode associated metadata. In order to reduce the cost of the transcoder/converter (which is implemented within a set-top box for example), the computational complexity of the conversion between the first audio codec system and the second audio codec system should be low. In the case of transcoding metadata, the computational complexity of the conversion between the first audio codec system and the second audio codec system should also be low. In this document, methods and systems for transcoding are described which enable metadata to be transcoded with reduced computational complexity.

Contents of the invention

According to one aspect, a transcoder is described that is configured to transcode an inbound bitstream into an outbound bitstream. The inbound bitstream may include inbound content frames and associated inbound metadata frames. The associated inbound metadata frame may be included in the inbound bitstream immediately following or immediately preceding the inbound content frame. As such, the term "associated" may mean a temporal relationship between a content frame and a metadata frame (eg, the term may mean that a content frame immediately precedes a metadata frame or vice versa). It should be noted that in some implementations, the associated inbound metadata frame may be included in the inbound content frame. Typically, a content frame includes a first element (eg, a synchronization field) and a last element (eg, an error correction field such as a CRC field). The associated metadata frame may be located in a field of the content frame arranged after the first element of the content frame and before the last element of the content frame (eg, in an ancillary data field of the content frame).

Metadata frames can be so-called evolved frames. Typically, an inbound bitstream includes a sequence of inbound content frames and a sequence of associated inbound metadata frames. Typically, inbound metadata frames alternate with inbound content frames such that a particular inbound content frame's associated metadata frame directly follows that particular inbound content frame. In a similar manner to the inbound bitstream (also called encoded inbound bitstream), the outbound bitstream (or encoded outbound bitstream) may include outbound content frames and associated outbound metadata frames. Specifically, the outbound bitstream may include an alternating sequence of outbound content frames and a sequence of outbound metadata frames.

Content frames may represent signals encoded according to a specific codec scheme. In particular, inbound content frames may represent signals encoded according to a first codec system, and outbound content frames may represent signals encoded according to a second codec system. The first audio codec system and the second audio codec system may be the same (in which case the transcoder may be configured to provide bitrate conversion) or the first audio codec system and the second audio codec system The transcoder system may be different (in which case the transcoder may be configured to provide codec conversion). The signal may include an audio signal. Examples of first and second codec systems are Dolby E, Dolby Digital Plus, Dolby Digital, Dolby TrueHD, Dolby Pulse, AAC (Advanced Audio Coding) and/or HE -AAC (High Efficiency AAC). Where the first codec system and the second codec system are different, the transcoder may be configured to transcode the signal content from the first codec system to the second codec system. Alternatively or additionally, the bitrate of the outbound bitstream may be different from the bitrate of the inbound bitstream, and the transcoder may be configured to perform transcoding of the encoded signal content from a first bitrate to a second (different) Bitrate transcoding.

Typically, a signal is represented as a sequence of frames including a predetermined number of samples of the signal (eg, 512 or 1024 samples of the signal). In this way, the inbound content frame may represent some or all samples of the signal's frames. Outbound content frames can represent some or all samples of the same frame of the signal. As such, the transcoder may be configured to generate outbound content frames that represent at least some samples of corresponding inbound content frames.

To transcode the inbound bitstream into the outbound bitstream, the transcoder may include a decoder configured to decode the inbound bitstream according to the first codec system. As a result of decoding, the decoder can provide a set of PCM samples for each content frame. Additionally, the decoder may be configured to extract metadata from the metadata frame. The decoded inbound bitstream (eg, a set of PCM samples and extracted metadata) may be provided to an encoder configured to encode the signal according to the second codec system, thereby providing an outbound bitstream. As such, the transcoder may be configured to generate outbound content frames from the inbound content frames using the decoder of the first codec system and the encoder of the second codec system. The transcoder may comprise a so-called PCM connected transcoder, in which a decoder passes groups of PCM samples to the encoder of the transcoder. As such, the transcoders described herein may include features described in the context of PCM connected transcoders.

It should be noted that content frames may also represent metadata according to the underlying codec system. In other words, the content frame may include metadata associated with a signal included in the content frame, wherein the metadata included in the content frame is configured by an implicit codec system (i.e., a first codec system or a second codec system). system). In contrast, metadata frames enable the transmission of additional metadata (in addition to the metadata specified by the codec system). Examples of such metadata are loudness or dialogue normalization parameters or ancillary data such as firmware upgrades for decoders in the audio content distribution chain.

Metadata frames can follow a predetermined syntax. Specifically, inbound metadata frames and outbound metadata frames may follow a common syntax. The syntax of the metadata frame may be such that the metadata frame can include zero metadata blocks, one or more metadata blocks. Each metadata block can include a specific type of metadata. As such, the metadata frame may be of variable size, depending on the amount of metadata and/or the number of metadata blocks included in the metadata frame. Each metadata block may represent (or may include) a corresponding descriptor that represents one or more attributes of the metadata included in the corresponding metadata block. Specifically, the descriptor may describe attributes that represent how the metadata block can or should be manipulated. This way, the transcoder can use the chunk's descriptor to transcode the chunks included in the inbound metadata frame in a computationally efficient manner.

To transcode a metadata frame, the transcoder may be configured to identify an inbound block of metadata from the inbound metadata frame. Inbound blocks can be identified using block identifiers. As an example, each chunk of the metadata frame can be identified using a chunk identifier. Furthermore, the metadata frame may include a specific chunk identifier that represents the fact that the metadata frame does not include any further chunks (eg, called an end identifier). The transcoder can use the end identifier to determine that the metadata frame does not include any additional metadata chunks.

As mentioned above, metadata inbound blocks may be associated with descriptors called inbound descriptors. An inbound descriptor may represent one or more properties of metadata included in the metadata inbound block. The descriptor can be written into the data field of the metadata block. An example attribute included within the descriptor is a timestamp parameter representing a sample of the signal. In particular, the timestamp parameter may represent the metadata of the inbound block associated with (eg, to be applied to) a sample of the signal identified by the timestamp parameter. The timestamp parameter may identify the sample by representing the position of the sample in the content frame relative to the end of the content frame or relative to the beginning of the content frame. A further example is a duration parameter representing several samples of a signal. The duration parameter may represent that the metadata of the inbound block is associated with a number of samples of the signal represented by the duration parameter (starting from the sample represented by the timestamp parameter). Specifically, the duration parameter may represent that the metadata is to be applied to a number of samples following the sample represented by the timestamp parameter, wherein the number of samples is represented by the duration parameter. The timestamp parameter and/or the duration parameter may be used, for example, to indicate to which samples of the signal encoded in the associated inbound content frame the metadata (eg, loudness value) of the inbound block may be applied. As an example, an inbound metadata frame may include multiple inbound blocks representing different loudness values for different sets of signal samples that are encoded in the inbound content frame.

Another example of an attribute represented (or included) within the descriptor is a transcoder parameter that indicates whether the inbound chunks are to be transcoded into an outbound bitstream. As an example, transcoder parameters can be used to indicate that the metadata included in the inbound block is only applicable to the first codec system. In this way, the transcoder may be configured to discard metadata included in the inbound chunks if the outbound bitstream is encoded according to a second codec system different from the first codec system.

Yet another example of an attribute included in the descriptor is the replication parameter, which indicates whether the inbound block's metadata is to be included in each outbound metadata frame generated from the inbound metadata frame. In a similar way, the deduplication parameter can be used as an attribute that indicates whether the metadata for the inbound chunk is to be discarded by the transcoder if an outbound metadata frame is generated from multiple inbound metadata frames. In cases where the inbound and outbound bitstreams are framed differently, the transcoder may use duplication parameters and/or deduplication parameters.

Yet another example of an attribute is a priority parameter that represents the importance of an inbound block of metadata relative to one or more other inbound blocks of metadata. The transcoder can use priority parameters where only a reduced amount of metadata can be inserted into the outbound bitstream compared to the inbound bitstream. A further example of a property is an association parameter indicating whether the inbound block's metadata can be inserted into a delayed outbound metadata frame following the outbound metadata frame. In this way, the correlation parameters provide the transcoder with additional flexibility in the transcoding process because the transcoder can determine in an efficient manner which inbound chunks can be delayed and which inbound blocks associated with the associated content frame must be retained. Station blocks.

Another example of an attribute is a PCM processing parameter that indicates whether the metadata of an inbound chunk is to be discarded by the transcoder if modifications to the data included in the inbound content frame are made. Specifically, the PCM processing parameters may indicate to the transcoder that the metadata of the inbound block is to be included in the outbound content frame even if the data of the inbound content frame (e.g., the signal samples included in the inbound content frame) have been modified. metadata frame. This may be the case, for example, when the inbound block includes payload such as binary data or like an additional bitstream that is not related to the data included in the inbound content frame. PCM processing parameters are particularly relevant for so-called PCM connection transcoders.

Preferred inbound descriptors include at least an indication of whether a timestamp parameter and/or a duration parameter are included in the descriptor. Additionally, preferred inbound descriptors include replication parameters and de-replication parameters.

The transcoder can be configured to generate outbound metadata frames from inbound metadata frames based on the inbound descriptor. Specifically, the transcoder may be configured to generate an outbound metadata frame from the inbound metadata frame based solely on one or more attributes represented by the inbound descriptor. More specifically, the transcoder may be configured to generate an outbound metadata frame from the inbound metadata frame without analyzing the metadata included in the inbound block. In this way, the transcoder can perform transcoding of the metadata included in the metadata frame based solely on the descriptor of the metadata chunk, without the need to analyze and/or parse the metadata carried by the metadata chunk. This allows the transcoder to have significantly reduced computational complexity.

The transcoder may be configured to generate outbound metadata from an inbound metadata frame by copying metadata from one or more inbound chunks of the inbound metadata frame to a corresponding one or more outbound chunks. Station metadata frame. One or more outbound blocks can be inserted into the outbound metadata frame. Copies and inserts may be subject to one or more attributes represented by the inbound descriptor of one or more inbound blocks. As an example, correlation parameters may indicate to the transcoder that specific inbound chunks are to be inserted into outbound metadata frames. On the other hand, the transcoder parameters may indicate to the transcoder that specific inbound blocks should be discarded if the second codec system is different from the first codec system.

The transcoder may be configured to generate an outbound metadata frame by generating an outbound descriptor for an outbound block based on the inbound descriptor of the inbound block. Specifically, an outbound descriptor may include or may represent some or all of the attributes represented by an inbound descriptor. Some or all properties of the inbound descriptor can be copied to the outbound descriptor. On the other hand, the transcoder may be configured to modify one or more attributes represented by the inbound descriptor to generate an outbound descriptor, where the outbound descriptor represents the one or more modified attributes. . As an example, an inbound descriptor can represent a timestamp parameter. The transcoder may modify the timestamp parameters such that even though the transcoder may have re-framed the outbound bitstream for the inbound bitstream, the modified timestamp parameters still represent the same timestamp parameters as the original timestamp parameters same signal sample.

As mentioned above, one or more properties of the inbound descriptor may include a timestamp parameter representing a signal sample with which the metadata of the inbound block is associated. The timestamp parameter of the inbound descriptor typically represents a signal sample associated with the inbound content frame. The transcoder can be configured to generate outbound chunks based on inbound chunks. Additionally, the transcoder may be configured to generate an outbound descriptor for an outbound block by modifying the timestamp parameter of the inbound descriptor such that the corresponding timestamp parameter of the outbound descriptor represents the same representation as the outbound Signal samples related to content frames (which may have different framing compared to inbound content frames). In this way, the transcoder can be configured to ensure that one or more attributes represented by the inbound descriptor remain valid even when the inbound bitstream is reframed.

The transcoder may be configured to insert outbound blocks (generated from the inbound blocks of the inbound metadata frame) into the delayed outbound metadata frame. As an example, the associated parameters of the inbound descriptor may indicate to the transcoder that the inbound block may be delayed. The transcoder may choose to insert metadata into delayed outbound metadata frames (eg, due to the limited bitrate of the second bitstream). A delayed outbound metadata frame may be associated with a delayed outbound content frame that does not include the signal sample represented by the timestamp parameter of the inbound block. Nonetheless, to ensure that the timestamp parameter of the outbound block identifies the correct signal sample, the transcoder can be configured to generate the outbound descriptor of the outbound block by modifying the timestamp parameter of the inbound block such that The timestamp parameter of the outbound descriptor represents a signal sample associated with a delayed outbound content frame. As an example, the modified timestamp parameter may represent a number of samples that exceeds the number of samples of the delayed content frame, thereby indicating that samples of the signal are present outside the delayed content frame.

As described above, one or more attributes of the inbound indicator may include a replication parameter that indicates whether the metadata for the corresponding inbound block is to be included in each outbound element generated from the inbound metadata frame. in the data frame. The transcoder can be configured to generate multiple outbound metadata frames based on the inbound metadata frame by taking into account replication parameters. In particular, the transcoder may be configured to determine that the replication parameter represents an inbound block of metadata to be included in each outbound metadata frame generated from the inbound metadata frame. In such a case, the transcoder may be configured to insert the metadata of the inbound chunk into each of the plurality of outbound metadata frames. Specifically, the transcoder may be configured to generate an outbound block based on the inbound block for each of the plurality of outbound metadata frames. In addition to generating multiple outbound metadata frames, the transcoder can be configured to generate multiple outbound content frames based on the inbound content frame, where the multiple outbound content frames can be individually associated with multiple outbound metadata frames. frame associated.

The replication parameters may include a flag that may be set to indicate that the inbound chunk's metadata is to be included in each outbound metadata frame generated from the inbound metadata frame, or that the inbound chunk's metadata is not to be Included in every outbound metadata frame generated from an inbound metadata frame (i.e., the flag may instead be set to indicate the opposite).

As mentioned above, one or more properties of the inbound descriptor may include a deduplication parameter that represents the metadata of the inbound block if an outbound metadata frame is generated from multiple inbound metadata frames. Whether it can be (or is to be) discarded by the transcoder. The transcoder may be configured to generate outbound metadata frames from multiple inbound metadata frames of the inbound bitstream by taking into account deduplication parameters. Specifically, a plurality of inbound metadata frames may include a plurality of inbound metadata blocks, each inbound block being associated with a corresponding deduplication parameter indicating that the inbound block's metadata may be discarded by the transcoder. The transcoder may be configured to: all inbound metadata frames except inbound metadata frames), discarding multiple inbound chunks of metadata to generate outbound metadata frames. In addition to generating outbound metadata frames from a plurality of inbound metadata frames, the transcoder may be configured to generate an outbound content frame from a plurality of inbound content frames, wherein the plurality of inbound content frames are respectively associated with the plurality of inbound metadata frames. Station metadata frame associated.

The deduplication parameters may include a flag that may be set to indicate that if an outbound metadata frame is generated from multiple inbound metadata frames, the metadata for the inbound block may be (or is to be) discarded by the transcoder; Or if an outbound metadata frame is generated from multiple inbound metadata frames, the inbound chunk's metadata may not be (or should not be) discarded by the transcoder (i.e., instead, the flag may be set to indicate the opposite Case).

As discussed above, one or more attributes of the inbound descriptor may include a priority parameter that represents the relative importance of the inbound block's metadata relative to one or more other inbound blocks of metadata. . The inbound metadata frame received at the transcoder may include multiple inbound blocks with descriptors representing different values of the priority parameter. The transcoder can be configured to generate outbound metadata frames based on multiple inbound chunks according to their priority parameters. Specifically, if a sufficient bitrate is available for the outbound bitstream, the transcoder may first select the one or more inbound chunks with the highest relative priority and only insert the lower priority inbound chunks piece.

Multiple inbound blocks can be associated with a delta priority parameter that represents delta priority. Multiple inbound chunks may include incremental metadata such that the combined metadata of the multiple inbound chunks provides high quality metadata and such that the metadata of the inbound chunk with the highest relative priority among the multiple inbound chunks provides quality Degraded metadata (i.e., providing metadata of reduced quality compared to the high-quality metadata provided by combined metadata). The inbound block with the next lower priority may provide metadata of increasing quality, and so on, until the highest quality metadata is provided when multiple inbound blocks are all combined. The transcoder may be configured to generate an outbound metadata frame based on at least one or more of the plurality of inbound blocks, thereby allowing scalability of the quality of metadata included in the outbound metadata frame ( scalable) degradation. The degree of degradation may be based, for example, on the available bitrate of the outbound bitstream.

As mentioned above, one or more properties of the inbound descriptor may include an association parameter indicating whether metadata for the inbound block may be inserted into delayed outbound metadata following the outbound metadata frame. frame. The transcoder may be configured to insert metadata from the inbound chunk into the outbound metadata frame based on correlation parameters and/or based on bitrate limits on the outbound bitstream. Specifically, the transcoder may be configured to insert metadata from the inbound block into a delayed outbound metadata frame following the outbound metadata frame if the associated parameter indicates that the inbound block's metadata may be delayed. middle.

According to another aspect, a method for transcoding an inbound bitstream including an inbound content frame and an associated inbound metadata frame into an outbound bitstream is described. The outbound bitstream may include outbound content frames and/or associated outbound metadata frames. Inbound content frames may represent signals encoded according to a first codec system, and outbound content frames may represent signals encoded according to a second codec system. As mentioned above, the first codec system and the second codec system may be the same or may be different. The method may include identifying an inbound block of metadata from an inbound metadata frame. The metadata inbound block may be associated with an inbound descriptor representing one or more properties of the metadata included in the metadata inbound block. Additionally, the method may include generating an outbound metadata frame from the inbound metadata frame based on the inbound descriptor. In other words, the outbound metadata frame can be determined by considering the inbound descriptor, often without further analysis of the metadata included in the inbound metadata frame.

According to another aspect, an encoded bitstream is described that includes content frames and associated metadata frames. The content frame may represent a signal encoded according to the first codec system. A metadata frame may include a metadata block, and the metadata block may be associated with (or may include) a descriptor representing one or more attributes of the metadata included in the metadata block.

According to another aspect, an encoder is described configured to generate an encoded bitstream including a content frame and an associated metadata frame. Content frames may represent signals encoded according to a codec system. Encoders can be configured to generate chunks of metadata. Additionally, the encoder may be configured to determine descriptors associated with metadata chunks. A descriptor may represent one or more properties of the metadata included in the metadata block. Additionally, the encoder may be configured to insert metadata blocks into metadata frames. It should be noted that the features described in this document in the context of transcoders also apply to the corresponding encoders.

Specifically, one or more attributes may include a timestamp parameter representing a signal sample to which metadata included in the metadata block is associated. Signal samples may be included in content frames. The encoder may be configured to insert blocks into delayed metadata frames, where the delayed metadata frames are associated with delayed content frames that do not include signal samples. Furthermore, the encoder may be configured to generate descriptors of metadata chunks such that the timestamp parameters of the descriptors represent signal samples related to delayed content frames. In this way, the encoder can be configured to delay the transmission of metadata and modify the timestamp parameters accordingly, thereby smoothing the bitrate of the bitstream generated by the encoder.

According to one aspect, a corresponding decoder is described. The decoder may include any of the decoder-related features described in this document. The decoder may be configured to decode an encoded bitstream including content frames and associated metadata frames. As mentioned above, the content frame represents a signal encoded according to the first codec system. A metadata frame may include a metadata block, wherein the metadata block is associated with (or includes) a descriptor representing one or more attributes of the metadata included in the metadata block. The decoder may be configured to decode the encoded signal included in the content frame. In particular, the decoder may comprise a decoder of the first codec system to decode the encoded signal. Therefore, the decoder may be configured to provide a set of PCM samples of the encoded signal.

Furthermore, the decoder may be configured to identify metadata blocks from the metadata frame and extract descriptors from the metadata blocks. Additionally, the decoder may be configured to process metadata included in the metadata block based on one or more attributes represented by the descriptor. One or more attributes may correspond to any one or more attributes described in this document. The decoder may be configured to associate specific attributes of the metadata with corresponding processing of the metadata. As an example, the descriptor may represent a timestamp parameter, thereby informing the decoder that the metadata of the metadata block is to be applied to a specific signal sample. In this way, the decoder can be configured to apply metadata to the samples represented by the timestamp parameter. As another example, a descriptor may represent an associated parameter. If the association parameter indicates that the metadata block is not related to the content frame, the decoder may be configured to pass the metadata included in the metadata block to another processing unit (which processes eg ancillary data included in the metadata block).

According to another aspect, a method for decoding an encoded bitstream including a content frame and associated metadata frame is described. The content frame may represent a signal encoded according to the first codec system. A metadata frame may include a metadata block, where the metadata block may be associated with a descriptor representing one or more attributes of the metadata included in the metadata block. The method may include decoding an encoded signal included in the content frame. Additionally, the method may include identifying metadata chunks from the metadata frame and extracting descriptors from the metadata chunks. Additionally, the method may include processing metadata included in the metadata block based on one or more attributes represented by the descriptor.

According to another aspect, a method for generating an encoded bitstream including a content frame and associated metadata frame is described. Content frames may represent signals encoded according to a codec system. The method may include generating a metadata block. Additionally, the method may include determining a descriptor associated with the metadata block, wherein the descriptor represents one or more attributes of metadata included in the metadata block. Additionally, the method may include inserting the metadata block into the metadata frame.

According to another aspect, an encoder is described that is configured to generate an encoded bitstream that includes content frames and associated metadata frames. The content frame may represent a signal encoded according to the first codec system. Encoders can be configured to generate chunks of metadata. In a preferred embodiment, the metadata block includes descriptors as described in this document. A descriptor may represent one or more properties of the metadata included in the metadata block.

The encoder may be configured to insert metadata blocks into metadata frames. Additionally, the encoder may be configured to select a security key from a plurality of predetermined security keys. Multiple predetermined security keys can be configured so as to provide different levels of trust. In particular, the plurality of predetermined security keys may include a high level of security known only to the developer of the encoder (or the developer of the corresponding decoder or the corresponding transcoder including the decoder and the encoder) Secret key. Furthermore, the plurality of predetermined security keys may include medium security keys known to the operator of the encoder (or the operator of the corresponding decoder or the corresponding transcoder including the decoder and the encoder) .

The encoder may be configured to generate an encrypted value based on at least the content frame, the associated metadata frame, and the selected security key. Specifically, the encoder may be configured to calculate a HMAC-MD5 value or a HMAC-SHA256 value (such as the secure hash algorithm specified in Federal Information Processing Standard FIPS PUB 180-2) to generate an encrypted value. Additionally, the encoder may be configured to truncate the HMAC-MD5 value or the HMAC-SHA256 value to produce an encrypted value. By truncating the HMAC value, you reduce the overhead required to encrypt the value. The encoder may be configured to insert the generated encrypted value into the metadata frame, thereby ensuring that the content frame and/or the metadata frame cannot be modified by unauthorized parties without detection.

The use of different security keys providing different levels of trust ensures that the corresponding decoder (or transcoder including the decoder) can verify whether the received bitstream has been modified, and if so, which party Modified received bitstream. As an example, the encoder might have originally generated the bitstream using a highly secure key. The intermediary party may have modified the bitstream and may have used a medium security key to generate the modified encrypted value. In this way, the decoder learns that the received bitstream has been modified by a party with access to a moderately secure key. It should be noted that multiple predetermined security keys may include more than two levels of trust, thereby providing the decoder with more details about the trust level of the received bitstream.

The encoder may be configured to insert a representation of the selected security key into the metadata frame so that the corresponding decoder can easily verify whether the received bitstream has been modified. On the other hand, the decoder may be configured to use all of the plurality of predetermined security keys to verify the authenticity of the received bitstream without inserting a representation of the selected security key into the element. in the data frame.

The encoder may be configured to generate a plurality of consecutive content frames and associated metadata frames for the encoded bitstream. Additionally, the encoder may be configured to generate a frame encryption value based on a single content frame and its associated metadata frame and based on a selected security key. The frame encryption value can be inserted into the associated metadata frame, and the corresponding decoder (or transcoder) can use the frame encryption value to verify the authenticity of the individual content frame/metadata frame. Furthermore, the encoder may be configured to generate historical encryption values based on at least some of the plurality of consecutive content frames and their associated metadata frames and based on the selected security value. The historical encryption value can be inserted into one of multiple consecutive metadata frames, and the corresponding decoder (or transcoder) can use the historical encryption value to verify multiple consecutive content frames and metadata frames the correct sequential order.

According to another aspect, a method for generating an encoded bitstream including a content frame and associated metadata frame is described. The content frame may represent a signal encoded according to the first codec system. The method may include generating a metadata block and inserting the metadata block into a metadata frame. Additionally, the method may include selecting a security key from a plurality of predetermined security keys, wherein the plurality of predetermined security keys provide different levels of trust. Additionally, the method may include generating an encrypted value based on at least the content frame, the associated metadata frame, and the selected security key. The resulting encrypted value can then be inserted into the metadata frame.

According to another aspect, a corresponding decoder is described. The decoder may be configured to receive an encoded bitstream including content frames and associated metadata frames. An encoded bitstream may have any one or more of the properties described in this document. In particular, the content frame may represent a signal encoded according to a first codec system (eg a codec system as mentioned in this document). The decoder can be configured to extract encrypted values from the metadata frame. The corresponding encoder may have inserted the encrypted value into the metadata frame as described in this document. In particular, the encrypted value may be determined using one of a plurality of predetermined security keys. As mentioned above, multiple predetermined security keys can provide different levels of trust. As an example, the plurality of predetermined security keys may include a high security key and a medium security key.

The decoder may be configured to determine the security key from a plurality of predetermined security keys. Specifically, the decoder may be configured to determine the security key by extracting the security key from the metadata frame (eg, from a specific field of the metadata frame). Furthermore, the decoder may be configured to generate a verification encrypted value based at least on the received content frame, the received associated metadata frame, and the determined security key. Additionally, the decoder may be configured to compare the extracted encrypted value with the verified encrypted value to determine whether the received encoded bitstream can be trusted. As an example, if the extracted encrypted value and the verified encrypted value match, the decoder may determine that the received encoded bitstream can be trusted. Additionally, the security key used to generate the authenticated encrypted value may indicate to the decoder the level of trust associated with the received encoded bitstream. As an example, a high security key can represent a higher level of trust than a medium security key.

The decoder may be configured to determine which of a plurality of predetermined security keys has been used to generate the extracted encrypted value. As mentioned above, the security key that has been used to generate the extracted encrypted value can provide an indication of the level of trust in the received encoded bitstream. Specifically, the decoder may be configured to generate a plurality of verification encryption values for a plurality of predetermined security keys respectively. Additionally, the decoder may be configured to compare each of the plurality of verified encrypted values to the extracted encrypted value. Additionally, the decoder may be configured to determine that one of the plurality of predetermined security keys has been used to generate the extraction if the comparison shows that one of the plurality of verified encrypted values matches the extracted encrypted value. encrypted value.

According to another aspect, a method for determining a trust level of a received encoded bitstream including a content frame and associated metadata frame is described. The content frame may represent a signal encoded according to the first codec system. The method may include extracting the encrypted value from the metadata frame. Additionally, the method may include determining a security key based on a plurality of predetermined security keys, wherein the plurality of predetermined security keys provide different levels of trust. Additionally, the method may include generating a verification encrypted value based at least on the content frame, the associated metadata frame, and the determined security key. The method may perform a comparison of the extracted encrypted value with the verified encrypted value to determine a trust level of the received encoded bitstream, where the trust level may be represented by a determined security key.

According to another aspect, a transcoder is described that is configured to transcode an inbound bitstream including an inbound content frame and an associated inbound metadata frame into an outbound bitstream. A transcoder may include any of the features described in this document related to transcoders. As mentioned above, the inbound bitstream may represent a set of signal samples, such as samples representing frames of a signal. The transcoder may include a decoder for decoding the received inbound bitstream and an encoder for re-encoding the decoded inbound bitstream to provide a transcoded outbound bitstream. Transcoders may include so-called PCM connection transcoders.

The decoder of the transcoder may be configured to convert the inbound content frame into a set of decoded PCM samples of the signal. Additionally, the decoder may be configured to extract metadata from inbound metadata frames. As such, the decoder may be configured to convert the inbound bitstream into a sequence of decoded PCM samples and associated metadata. The sequence of decoded PCM samples and associated metadata may be used by the transcoder's encoder to generate an outbound bitstream (according to the second codec system). The decoder may be configured to generate a signature value using the decoder security key for the set of decoded PCM samples and extracted metadata. The signature value can be generated using the HMAC-MD5 hash function or the HMAC-SHA256 hash function. The resulting value can be truncated to provide a signed value. In this way, the decoder can be configured to provide a signature value, thereby enabling the encoder to verify whether the decoded PCM samples and/or metadata between the transcoder's decoder and the encoder have been modified by an unauthorized entity ( It cannot obtain the decoder security key) modification.

The transcoder's encoder may be configured to receive a set of PCM samples and associated metadata. The received set of PCM samples typically corresponds to a decoded set of PCM samples provided by the decoder, and the received metadata typically corresponds to extracted metadata from the decoder. However, the PCM samples and/or metadata may have been modified such that the received set of PCM samples and/or received metadata may be different from the set of decoded PCM samples and/or extracted metadata.

The encoder can be configured to receive signed values. The received signature value may correspond to or be identical to the signature value generated by the decoder. On the other hand, the received signature value may differ from the signature value generated by the decoder (eg, if modified by an authorized entity, modifications to the PCM sample and/or metadata were made). The encoder may be configured to use the encoder security key to verify that the received signature value is valid for a received set of PCM samples and associated metadata. Furthermore, the encoder may be configured to, if the received signature is valid, generate an outbound content frame of the outbound bitstream based on the received set of PCM samples and generate an associated outbound content frame of the outbound bitstream based on the received metadata. Metadata frame. On the other hand, the encoder may be configured to prevent insertion of received metadata into the outbound bitstream if the received signature is invalid. In this way, the transcoder's encoder can be configured to prevent metadata frames from being inserted into the outbound bitstream if the metadata or PCM samples have been modified by an unauthorized entity.

It should be noted that typically, the decoders and encoders used in transcoders are provided by the developers of the corresponding audio codec systems. This way, decoder and encoder functionality can be controlled by developers, ensuring high-quality audio content and associated metadata. On the other hand, unauthorized entities can make modifications to PCM samples and/or metadata between the decoder and encoder, creating a risk of reduced quality of the audio content and/or metadata. By providing a decoder that generates a signature value and by providing an encoder that verifies the signature value, it is ensured that unauthorized modifications to PCM samples and/or metadata can be detected.

The encoder can be configured to use the decoder security key as the encoder security key. This ensures that the encoder can verify that the received PCM samples and metadata correspond to those provided by the corresponding decoder.

The transcoder may further include a PCM processing stage configured to modify a set of decoded PCM samples and/or extracted metadata to produce a set of second PCM samples and associated second metadata. The set of second PCM samples may correspond to a set of decoded PCM samples or a set of modified PCM samples. In a similar manner, the second metadata may correspond to extracted metadata or modified extracted metadata. Additionally, the PCM processing stage may be configured to communicate a second set of PCM samples and associated second metadata to the encoder. By using the received signature value and the encoder security key, the encoder may be configured to detect that the decoded PCM samples and/or the extracted metadata have been modified by the PCM processing stage. In other words, the encoder may be configured to detect that the second PCM sample (received by the encoder) and the second metadata (received by the encoder) do not correspond to the decoded PCM sample and extracted metadata (provided by the decoder) .

The transcoder may further include a re-signing unit configured to use the re-signed security key to determine an updated signature value for a second set of PCM samples and associated second metadata. Furthermore, the re-signing unit may be configured to communicate updated signature values to the encoder. The re-signing security key can be different from the decoder security key. The encoder can be configured to use the re-signed security key as the encoder security key. In this way, the encoder may be configured to detect that PCM samples and/or associated metadata have been modified by an authorized PCM processing level. In a similar manner to the encrypted values described in this document, the security key used to sign the value may be selected from a plurality of predetermined security keys. As an example, the decoder security key may be a high security key and the re-signed security key may be a medium security key, thereby targeting the PCM samples and/or associated elements received at the encoder of the transcoder. Data offers different levels of trust.

The encoder of the transcoder may include a PCM processing stage configured to modify a set of received PCM samples and/or received metadata. A set of received PCM samples may correspond to a set of decoded PCM samples or a set of second PCM samples. In a similar manner, received metadata may correspond to extracted metadata or secondary metadata. The encoder may be configured to generate outbound content frames and/or outbound content frames based on a modified set of received PCM samples and/or modified received metadata that have been modified by a PCM processing stage of the encoder. Station metadata frame. By providing the transcoder's encoder with a PCM processing stage, you ensure that the chain of trust is maintained within the transcoder (because the PCM processing is performed in the encoder provided by the encoder's developer).

As mentioned above, the PCM connection transcoder may include any of the features described in this document. Specifically, the decoder of the transcoder may be configured to identify metadata inbound chunks from inbound metadata frames. As described in this document, a metadata inbound block may be associated with an inbound descriptor representing one or more attributes of the metadata included in the metadata inbound block. The one or more attributes may be any one or more of the attributes described in this document. The transcoder's encoder may be configured to generate outbound metadata frames from inbound metadata frames based at least on the inbound descriptor.

Specifically, one or more attributes may include a PCM processing parameter indicating whether the incoming data is to be discarded by the encoder if a modification of a set of PCM samples and/or a modification of the extracted metadata is made. Metadata for the site block. In such cases, the transcoder's encoder may be configured to include or exclude the inbound block in the outbound metadata frame based on the value of the PCM processing parameter. Specifically, the encoder may be configured to: even if a set of PCM samples and/or extracted metadata has been modified, if the PCM processing parameters indicate that the metadata of the inbound block should not be discarded, then the metadata of the inbound block should not be discarded. The data is included in the outbound metadata frame. This may be useful for example where the metadata included in the inbound block is independent of a set of PCM samples (as in the case for example regarding ancillary data or binary data).

The PCM processing stage of the transcoder may be configured to provide a representation of one or more PCM processing conditions to the encoder of the transcoder. The one or more PCM processing conditions may represent how the PCM processing stage processed a set of PCM samples and/or extracted metadata. As an example, the one or more PCM processing conditions may include one or more of the following: conversion of the sample rate of a set of PCM samples, mixing of PCM samples with system sounds, modification of extracted metadata, a set of PCM Modification of the channel configuration of the samples (in the case of audio signals), leveling of the loudness of a set of PCM samples. The encoder may then be configured to generate outbound metadata frames from the inbound metadata frames based also on one or more PCM processing conditions. Specifically, the encoder may be configured to determine whether to include the inbound block in the outbound metadata frame or not to include the inbound block based on the value of the PCM processing parameter and based on one or more PCM processing conditions. In the outbound metadata frame. Specifically, PCM processing parameters may represent how inbound blocks are processed subject to one or more PCM processing conditions.

According to another aspect, a method for transcoding an inbound bitstream including an inbound content frame and an associated inbound metadata frame into an outbound bitstream is described. An inbound bitstream can represent a set of samples of a signal. The method may include converting the inbound content frame into a set of decoded PCM samples of the signal at the decoder. Additionally, the method may include extracting metadata from the inbound metadata frame at the decoder. Additionally, a decoder security key can be used to generate a signature value against a set of decoded PCM samples and extracted metadata. A set of decoded PCM samples, extracted metadata and generated signature values can be passed to the corresponding encoder. Additionally, the method may include receiving at the encoder a set of PCM samples and associated metadata and receiving a signature value. The method proceeds by using the encoder security key to determine whether the received signature value is valid for a received set of PCM samples and associated metadata. Thereafter, if the received signature is valid, an outbound content frame for the outbound bitstream may be generated based on the received set of PCM samples and an associated outbound metadata frame for the outbound bitstream may be generated based on the received metadata.

According to other aspects, the decoder and encoder of the above-mentioned PCM connection transcoder are described separately. The decoder and/or encoder respectively may comprise any one or more of the features described in this document in relation to decoders and/or encoders. Decoders and/or encoders may be used in transcoders (as described above). Alternatively or additionally, the decoder and/or encoder may be used separately. Thus, according to another aspect, a decoder is described that is configured to decode an inbound bitstream including an inbound content frame and an associated inbound metadata frame. An inbound bitstream can represent a set of samples of a signal. The decoder may be configured to convert the inbound content frame into a set of decoded PCM samples of the signal. Additionally, the decoder may be configured to extract metadata from inbound metadata frames. Additionally, the decoder may be configured to generate a signature value using the decoder security key for the set of decoded PCM samples and for the extracted metadata. In this way, a set of decoded PCM samples and associated extracted metadata can be protected using the signature value. Recipients of a set of decoded PCM samples and associated extracted metadata may use the signature value to verify that a set of decoded PCM samples and/or associated extracted metadata have been processed in an unspecified format. The authorization method has been modified. The receiver may be an encoder configured to re-encode a set of decoded PCM samples and associated extracted metadata into an outbound bitstream. Therefore, the decoder may be configured to send a set of decoded PCM samples, extracted metadata and generated signature values to the encoder for re-encoding.

According to another aspect, an encoder is described that is configured to encode an outbound bitstream including an outbound content frame and an associated outbound metadata frame. The encoder may be configured to receive a set of PCM samples and associated metadata and receive a signature value for the set of PCM samples and associated metadata. The received set of PCM samples may correspond to (or may be derived from) the set of decoded PCM samples described above. In a similar manner, the received set of associated metadata may correspond to (or may be derived from) the set of extracted metadata described above. The received signature value can be determined (eg, at the decoder) using the set of decoded PCM samples and extracted metadata described above.

The encoder may be configured to use the encoder security key to verify that the received signature value is valid for a received set of PCM samples and associated metadata. Furthermore, the encoder may be configured to, if the received signature is valid, generate an outbound content frame of the outbound bitstream based on the received set of PCM samples and generate an associated outbound content frame of the outbound bitstream based on the received metadata. Metadata frame.

According to another aspect, a method for decoding an inbound bitstream including an inbound content frame and an associated inbound metadata frame is described. An inbound bitstream can represent a set of samples of a signal. The method may include converting the inbound content frame into a set of decoded PCM samples of the signal and extracting metadata from the inbound metadata frame. Furthermore, the method may include generating a signature value using a decoder security key for the set of decoded PCM samples and for the extracted metadata. Additionally, the method may include providing the set of decoded PCM samples, extracted metadata and generated signature values to the encoder for re-encoding.

According to another aspect, a method for encoding an outbound bitstream including an outbound content frame and an associated outbound metadata frame is described. The method may include receiving a set of PCM samples and associated metadata and receiving a signature value for the set of PCM samples and associated metadata. Additionally, the method may include using the encoder security key to verify that the received signature value is valid for the received set of PCM samples and associated metadata. The method may proceed by, if the received signature is valid, generating an outbound content frame of the outbound bitstream based on the received set of PCM samples and generating an associated outbound metadata frame of the outbound bitstream based on the received metadata.

According to one aspect of the present application, an encoding method is provided, including: encoding the current content frame; generating a protection field for an associated metadata frame, the associated metadata frame being associated with the current content frame; encoding the metadata frame, including the protection field; and including the current content frame and the associated metadata frame in the output bitstream, wherein: generating the protection field involves generating one or more encrypted values; one or more encrypted values At least one of the values is a frame encryption value that represents authenticity of the current content frame; and the frame encryption value is generated by applying a one-way function to a set of frames including the current content frame and associated metadata frames.

According to another aspect of the present application, there is provided an encoding device comprising one or more hardware elements, the encoding device being configured to: encode a current content frame; generate a protection field for an associated metadata frame, associating the associated metadata frame with the current content frame; encoding the associated metadata frame, including a guard field; and including the current content frame and the associated metadata frame in the output bitstream, wherein: generating the guard field Involves generating one or more encrypted values; at least one of the one or more encrypted values being a frame encrypted value representing the authenticity of a current content frame; and by applying a one-way function to a frame including the current content frame and an associated A frame encryption value is generated from a set of frames of metadata frames.

According to another aspect of the present application, a method for transcoding an inbound bitstream into an outbound bitstream is provided, the inbound bitstream comprising a first inbound content frame and an associated first inbound metadata frame , the method includes: at the decoder: converting the first inbound content frame into a first set of decoded pulse code modulation (PCM) samples; extracting first metadata from the first inbound metadata frame; A first inbound block of metadata is identified in the metadata, the first inbound block of metadata being associated with a first inbound descriptor representing one or more attributes of the first metadata, the one or more attributes including PCM processing parameters, the PCM processing parameters represent the modification of the first group of decoded PCM samples, the modification of the extracted first metadata, or the modification of the first group of decoded PCM samples and the extracted whether the metadata of the first metadata inbound block is to be discarded by the encoder if both the first metadata and the first metadata are modified; generating a frame signature value based on the first set of decoded PCM samples and the first metadata; and transmitting the first set of decoded PCM samples, the first metadata and the frame signature value to the corresponding encoder; and at the encoder: receiving the first set of decoded PCM samples, the first metadata and the frame signature value; Determining whether the frame signature value is valid for the first set of decoded PCM samples and the first metadata; and determining, based at least in part on whether the frame signature value is valid: whether to generate an outbound bitstream based on the first set of decoded PCM samples. a first outbound content frame; and whether an associated first outbound metadata frame of the outbound bitstream is generated from the first inbound metadata frame based at least in part on the first inbound descriptor.

According to another aspect of the present application, a transcoder is provided, configured to: transcode an inbound bitstream including an inbound content frame and an associated inbound metadata frame to include an outbound content frame and an associated an outbound bitstream of outbound metadata frames; wherein the inbound content frame represents a signal encoded in accordance with a first codec system, and wherein the outbound content frame represents a signal encoded in accordance with a second codec system; wherein , the transcoder is configured to: identify a metadata inbound block from the inbound metadata frame; wherein the metadata inbound block is associated with an inbound block representing one or more attributes of the metadata included in the metadata inbound block. the inbound descriptor is associated; and the outbound metadata frame is generated from the inbound metadata frame based on the inbound descriptor.

According to another aspect, a software program is described. The software program may be adapted for execution on a processor and may be adapted to perform the method steps described in this document when executed on the processor.

According to another aspect, a storage medium is described. The storage medium may comprise a software program adapted for execution on a processor and adapted to perform the method steps described in this document when executed on the processor.

According to another aspect, a computer program product is described. The computer program may comprise executable instructions for performing the method steps described in this document when executed on a computer.

It should be noted that the methods and systems as described in this patent application, including preferred embodiments thereof, may be used alone or in combination with other methods and systems disclosed in this document. Furthermore, all aspects of the methods and systems described in this patent application may be combined in any way. In particular, the features of the present application can be combined with each other in any way.

Description of drawings

The invention is described below by way of example with reference to the accompanying drawing, in which:

Figure 1a shows a block diagram of an example audio content distribution chain including a transcoder;

Figure 1b shows an example structure of a metadata frame;

Figures 2a and 2b show examples of timestamp attributes used in metadata frames;

Figures 3a and 3b show examples of deduplication attributes used in metadata frames;

Figures 4a and 4b show examples of copy attributes used in metadata frames; and

Figures 5a-5d and 6 illustrate an example PCM connected transcoder.

Detailed ways

As described in the background section, audio content is typically associated with metadata, and the audio content is encoded into a joint bitstream that includes a sequence of encoded content frames and a sequence of associated metadata containers (also called metadata frames) middle. Figure 1 illustrates a block diagram of an example distribution system 100 for audio content. The methods and systems described in this document are outlined in the context of audio content. However, it should be noted that the method and system are applicable to other types of content such as video content. In a more general sense, the methods and systems described in this document are suitable for multimedia content such as audio and/or video, where the multimedia content is associated with metadata.

Distribution system 100 includes an encoder 101 configured to encode audio content and provide an encoded bitstream 110 (also referred to as first encoded bitstream 110 or inbound encoded bitstream 110). Typically, the first encoded bitstream 110 includes a sequence of encoded content frames 111 , where the encoded content frames 111 may be associated with corresponding metadata frames 112 . The encoder 101 is configured to provide a first encoded bitstream 110 encoded according to a first audio codec system. The first audio codec system may be, for example, one of: Dolby E, Dolby Digital Plus, Dolby Digital, Dolby TrueHD, Dolby Pulse, AAC and/or HE-AAC. Content frame 111 may represent or may include a predetermined number of samples of audio content, such as 1536, 1024, or 512 samples of audio content.

The first encoded bitstream 110 is provided to the transcoder 103 via a transmission medium or via a storage medium 102 . The transcoder 103 is configured to transcode or convert the first encoded bitstream 110 into a second encoded bitstream 120 (also referred to as the outbound bitstream 120), wherein the second encoded bitstream 120 is based on the second audio Encoded by the codec system. The second audio codec system may be different from the first audio codec system. On the other hand, the second audio codec system may be the same as the first audio codec, but use a different configuration, such as a different bit rate, a different frame rate, and/or a different channel configuration. The second audio codec system may be, for example, one of: Dolby E, Dolby Digital Plus, Dolby Digital, Dolby True HD, Dolby Pulse, AAC, and/or HE-AAC. In a similar manner to the first encoded bitstream 110, the second encoded bitstream 120 includes a sequence of content frames 121 and a corresponding sequence of metadata frames 122. The content frame 121 of the second encoded bitstream 120 may have a different frame size than the frame size of the content frame 111 of the first encoded bitstream 110 . The second encoded bitstream 120 may be provided to the decoder 104 for rendering audio content.

Metadata frames 112, 122 may have a predetermined structure. In other words, the metadata frames 112, 122 may follow a predetermined syntax. As an example, the metadata frames 112, 122 may follow the so-called evolved frame syntax shown in Table 1. The evolved frame syntax may be used, for example, in the context of standard multimedia content codec systems such as the Dolby Video Broadcast (DVB) system and/or the Moving Picture Experts Group (MPEG) codec system. It should be noted that the metadata frame syntax shown in Table 1 and the subsequent tables are only examples. Variations or modifications can be made to the grammar. In particular, the syntax shown in this document can be extended by, for example, additional fields to provide additional functionality.

Table 1

The semantics of the parameters of the evolving frame shown in Table 1 can be as follows:

• key_id may be the identifier of the encryption key used for hashing (i.e., used to calculate the protection_bits of the protection() field).

● payload_id can be the identifier of the payload of the following application; payload_idEND="0000b" can have the following meaning: no additional payload is included in this evo_frame();

●payload_size can represent the number of bytes in the following payload field.

The evolved frame syntax specifies a metadata frame 112, 122 that may include multiple metadata chunks, also referred to as payloads. As such, metadata frames 112, 122 may include zero metadata blocks, one or more metadata blocks, where each metadata block represents a specific metadata type and/or a specific metadata aspect. Examples of metadata types are:

• Descriptive metadata that describes specific aspects of the content frame 111 associated with the metadata frame 112 (e.g., tempo information and/or harmony information);

● Irrelevant metadata, which includes ancillary data not directly related to the content frame 111 (such as firmware upgrades of the target decoder encoding the audio content);

- Control metadata that may be used to control the rendering of one or more samples of content frame 111 associated with metadata frame 112 (eg, the loudness value of one or more samples of content frame 111).

In this way, the metadata frame 112 provides a flexible structure that can be extended by additional metadata blocks when needed to describe additional characteristics of the encoded audio content or to convey additional ancillary data in the bitstream 110. In the case that no metadata is to be transmitted along with the content frame 111, the metadata frame 112 may not include a metadata block. In the syntax of the evolved frame of Table 1, this may be represented by a predetermined "END" ID (identifier). Represented by the corresponding payload_id.

In this document, it is proposed to add descriptors to metadata blocks, wherein the descriptors describe one or more characteristics or attributes of the metadata included in the associated metadata block. In the syntax of the evolved frame shown in Table 1, this descriptor is called "payload_config()". The transcoder can then use the descriptor to perform efficient transcoding of the metadata chunk without parsing the metadata included in the associated metadata chunk. Therefore, the complexity of metadata transcoding can be significantly reduced.

In other words, this document describes a method of transcoding a block of metadata (also called a payload) within a metadata frame 112 (eg, within the evolved frame shown in Table 1) from one encoded bitstream to another. kind of bit stream. Transcoding operations may be directed by specific fields within each payload (for example, the field "payload_config()" of the metadata block as shown in Table 1). Transcoding operations can then be specified such that the respective payloads can be appropriately transcoded from one encoding stream to another without having to extract or parse the nature of the metadata chunk's implicit metadata parameters (i.e. , without extracting or parsing the underlying payload's essence).

Figure Ib shows an example structure of metadata frame 130 (eg, metadata frame 112). The metadata frame 130 may include a frame header 131 representing general information regarding the structure of the metadata frame 130 and the association between the metadata frame 130 and the content frame 111 of the encoded bitstream 110 . The frame header 131 may include some or all fields in the evolved frame of Table 1 that are not related to the payload of the frame. Additionally, metadata frame 130 may include one or more metadata blocks 140 (also referred to as metadata payload 140). The metadata block 140 may include a block header 141, which may represent the size of the metadata block 140 (referred to as payload_size in Table 1). Additionally, the metadata block 140 may include a descriptor 142 (referred to as payload_config() in Table 1), where the descriptor 142 may represent a type of metadata and/or one or more attributes of the metadata, the metadata including In data field 143 of metadata block 140 (ie, payload() shown in Table 1).

An example descriptor 142, ie, an example "payload_config()" field, for the metadata block 140 of the evolved frame is shown in Table 2. It can be seen that descriptor 142 may include or may represent one or more attributes of the metadata included in block 140 . In the example in Table 2, the attributes are:

• The metadata of block 140 can be adapted to timestamp parameters representing samples of audio content. The timestamp may represent a sample included in the content frame 111 associated with the metadata frame 112 of block 140 . Alternatively or additionally, the timestamp may be configured to have a value large enough to represent samples included in the content frame subsequent to the content frame 111 associated with the metadata frame 112 of block 140 .

• The metadata of block 140 can be adapted to a duration parameter representing a number of samples (starting from a sample represented by a timestamp).

• A transcoding flag (referred to as the "do not transcode" flag in Table 2) that provides instructions to the transcoder as to whether the metadata block 140 is to be transcoded. If the "do not transcode" flag is set, the transcoder may simply ignore or remove the metadata chunk 140 when transcoding the inbound bitstream 110. This may be useful where the metadata is relevant only to the first codec system of the inbound bitstream 110 and is meaningless to any other codec system to which the bitstream 110 may be transcoded (as in e.g. The data included in the inbound bitstream 110 generates a cyclic redundancy check (CRC). Typically, the CRC is only meaningful if the encoded data has not been modified, so there is no need to transcode the CRC). In a more general sense, transcoding flags can be used to identify objects that are only useful during the decoding process of the inbound bitstream within a transcoder (thus not requiring a subsequent recoding process for generating the outbound bitstream. ) metadata.

• Copy flag that provides instructions to the transcoder whether to copy the metadata included in block 140 when the size of the content frame 111 is different before and after transcoding.

• Deduplication flag that provides instructions to the transcoder whether to remove copies of the metadata included in block 140 when the size of the content frame 111 is different before and after transcoding.

• A priority parameter that provides an indication of the relative importance of the metadata included in block 140. For example, if the allowed bitrate of the transcoded second bitstream 120 is reduced relative to the bitrate of the first bitstream 110 , the transcoder may use the priority parameter to select one or more from the metadata frame 130 More blocks 140.

• Association flag (referred to as the "now_or_never" flag in Table 2) that provides an indication to the transcoder whether the metadata included in block 140 is associated with the corresponding content frame 111. This way, if the "now_or_never" flag is set, the transcoder learns the fact that the metadata included in block 140 should be transcoded immediately or should be discarded (because the "now_or_never" flag indicates that if the metadata is delayed, then The decoder cannot use metadata).

Table 2

In other words, the semantics of the attribute parameters of descriptor 142 shown in Table 2 can be as follows:

• a timestamp parameter representing the offset of the sample from the beginning of the content frame 111 to which the payload 143 in question belongs;

● a duration parameter, indicating the time in the sample for which the payload 143 in question is still valid;

● dont_transcode flag, which marks whether the payload in question 143 must be discarded when transcoded (flag=1) or whether transcoding can occur (flag=0);

● Copy flag, when set to 1, this flag signals that the payload 143 in question needs to be copied during transcoding such that the payload 143 appears in the transcoded time between timestamp and timestamp plus duration in block 140. A copy flag may be set, for example, for loudness data to indicate that the frames have the same dialogue normalization. In a more general sense, replication flags can be set for time-agnostic metadata. Typically, the copy flag is not set for data that itself supports the concept of time, like the bitstream of a codec for example. In other words, metadata that is internally timed may not be provided with a set replication flag and/or deduplication flag, where the term "internally timed" means that only the exact sequence of metadata blocks is meaningful, i.e. Copying or deduplication will invalidate the metadata. An example of internally timed metadata is a different bitstream (different from the content included in the content frame) embedded in a sequence of metadata blocks of a sequence of metadata frames. The payload of such a bitstream should never be copied or decopied. Otherwise, the bitstream will be partially repeated or partially cut. Another example of internally timed data is binary data such as executable programs. If such binary data is transmitted in multiple metadata chunks across multiple metadata frames, copying or deduplication of the metadata chunks will invalidate the meaning of the binary data.

● Deduplication flag: The deduplication flag ensures that during transcoding, every metadata with a specific id in the same outbound metadata frame is deleted except for the first metadata block where the flag is set to 1. piece. Deduplication flags may be set, for example, for loudness data such as dialogue normalization that does not need to be presented multiple times for each outbound metadata frame 122 .

● The "now_or_never" flag, which indicates that the payload does not need to be delayed while transcoding.

● PCM processing parameters, referred to as "tight_coupling" parameters in Table 2. In the case of modifications to the samples of the signal included in the content frame, for example in the context of a PCM connection transcoder as described below, PCM processing parameters may be used to inform the PCM connection transcoder how to process information related to a specific content Metadata for the specific metadata frame associated with the frame. The function of PCM processing parameters is described in further detail below when describing the function of PCM connecting to the transcoder.

table 3

Table 3 shows the syntax of example data fields 143 of metadata block 140.

As discussed above, the bitstream syntax for carrying metadata (i.e., metadata frame 130 including metadata block 140) may define general metadata attributes (e.g., included in descriptor 142, i.e., as shown in Table 2 payload_config() field). These properties enable metadata to be encoded even if the first codec (used to encode the inbound bitstream 110) and the second codec (used to encode the outbound bitstream 120) use different framing. A simple copy is made from an inbound (i.e. first) bitstream 110 to an outbound (i.e. second) bitstream 120. The manner in which the copy of metadata is performed is guided by the attributes included in the descriptor 142 . The only thing that may need to change during the transcoding process may be the properties themselves. However, modification of the attributes included in the descriptor 142 does not require knowledge about the actual meaning of the metadata included in the data field 143 of the block 140 .

Below, the example properties shown in Table 2 are described in more detail. Specifically, how transcoder 103 may use one or more attributes represented by descriptor 142 to perform efficient transcoding of metadata included in metadata block 140 is described.

Figures 2a and 2b illustrate the use of the timestamp parameter included in the descriptor 142 of the metadata block 140. In Figure 2a, it is shown how the transcoder 103 may update the timestamp parameter 201 when transcoding metadata from the first bitstream 110 to the second bitstream 120. In the example shown, the timestamp parameter 201 represents the position of a particular sample 202 relative to the end of the associated content frame 111 (ie, relative to the most recent sample). As such, timestamp parameter 201 represents the "delay" of sample 202 relative to the most recent sample included in content frame 111. In the example shown in FIG. 2 , the content frame 121 of the second bitstream 120 has a different size from the content frame 111 of the first bitstream 110 . Specifically, the size of the content frame 121 of the second bitstream 120 is larger than that of the first bitstream 120 . The size of the content frame 111 of the bitstream 110. Therefore, the particular sample 202 may be located at a different relative position within the content frame 121 of the second bitstream 120 compared to the relative position within the content frame 111 of the first bitstream 110 . Specifically, a particular sample 202 may exhibit a different "latency" relative to the most recent sample included in the outbound content frame 121 than relative to the most recent sample included in the inbound content frame 111 . Therefore, when inserted into the metadata frame 122 of the second bitstream 120 , the timestamp parameter 201 included in the metadata frame 112 of the first bitstream 110 may need to be modified, thereby producing a transcoded timestamp parameter 203 .

Figure 2b shows the possibility of moving metadata blocks 140 in the bitstreams 110, 120. This can be used to smooth the bitrate of the bitstream 120 after transcoding. As an example, metadata for a particular block 140 in the metadata frame 112 may be associated with a particular sample 202 in the content frame 111 (represented by a timestamp parameter 211). As mentioned above, the location of a particular sample 202 may be expressed relative to the sample of the last, most recent inbound content frame 111 . If it is not necessary that the metadata for a particular chunk 140 arrives immediately after the content frame 121 including the sample 202 (as may be indicated by an association flag (referred to as the "now_or_never" flag in Table 2)), the transcoder may Specific block 140 moves to metadata frame 222 of content frame 221 following content frame 121 including sample 202 . The transcoder 103 may update the timestamp parameter 213 so that the timestamp parameter 213 points to the correct sample 202 .

Specifically, the timestamp parameter 213 may represent the position of the sample 202 relative to the last, ie, the most recent outbound content frame 221 sample with which the outbound metadata frame 222 that includes the timestamp parameter 213 is associated. For this purpose, the timestamp parameter 213 may have a value that exceeds the number of samples included in the content frame 221 . In a similar manner, the timestamp parameter 213 may be configured to have a negative value. Such negative values may be used to represent samples 202 included in future content frames, ie, samples 202 included in content frames subsequent to the content frame 221 associated with the metadata frame 222 including the timestamp parameter 213 . By doing so, the metadata may be transmitted prior to one or more samples to which the metadata is associated (eg, to which the metadata is to be applied).

In this way, the timestamp parameter 211 (possibly combined with an associated flag) enables the transcoder 103 to transmit metadata associated with the timestamp 211 in a subsequent metadata frame 222 or a previous metadata frame 222, and enables transcoding The processor 103 is able to adjust the timestamp 213 so that the timestamp 213 refers to the same PCM sample 202 (even after transcoding, the sample 202 is not included in the content frame 221 associated with the metadata frame 222 that includes the particular block 140). Therefore, the transcoder 103 is provided with some flexibility to smooth the bitrate of the second bitstream 120.

It should be noted that in a similar manner to the transcoder 103, the encoder 101 may be configured to include the metadata of the sample in subsequent metadata frames. As such, the encoder 101 may be configured to generate a timestamp 213 pointing to a sample 202 included in a content frame 121 that is not a content frame associated with a metadata frame that includes the timestamp 213 .

Figures 3a and 3b illustrate possible use cases for the deduplication flag represented by the descriptor 142 of the metadata block 140. In the scenario shown, the content frames 121 of the second bitstream 120 represent a higher number of samples (ie, have a higher frame size) than the content frames 111 of the first bitstream 110 . If the frame sizes are different, it may happen that a single content frame 121 of the second bitstream 120 includes samples from more than one content frame 111 of the first bitstream 110 . In such a case, the metadata chunk 140 may be obtained from more than one metadata frame 112 associated with more than one content frame 111 of the first bitstream 110 . The transcoder 103 must determine which of the metadata blocks 140 are to be included in the single metadata frame 122 of the single content frame 121 of the second bitstream 120 . The deduplication flag for a particular block 140 may indicate to the transcoder 103 that if the metadata blocks 140 from multiple metadata frames 112 of the first bitstream 110 are to be merged, the particular block 140 does not need to be inserted into the second bitstream 110 120 in metadata frame 122. As such, the transcoder 103 may be configured to discard or ignore the metadata chunks 140 of the additional metadata frame 112 that have the deduplication flag set.

This is illustrated in Figure 3a, where outbound content frame 121 (i.e., content frame 121 of outbound bitstream 120) includes inbound content frames 111 and 311 (i.e., content frames 111, 311 of inbound bitstream 110 ) sample. The transcoder 103 must determine which of the blocks 140 of the inbound metadata frames 112 , 312 (i.e., the metadata frames 112 , 312 of the inbound bitstream 110 ) are to be included in association with the outbound content frame 121 in the outbound metadata frame 122 (i.e., the metadata frame 122 of the outbound bitstream 120). In the example shown in Figure 3a, it is assumed that a deduplication flag is set for at least one or more blocks 140 of the inbound metadata frame 312. As such, transcoder 103 may be configured to discard block 140 of inbound metadata frame 312 .

It should be noted that a deduplication flag may also be set for one or more blocks 140 of the inbound metadata frame 112 . The transcoder 103 may be configured to discard only the blocks 140 used to create the second (or more) metadata frames 312 of the outbound metadata frame 122 . In other words, the transcoder 103 may be configured to consider the deduplication mark only when more than one inbound metadata frame 112 is to be considered for generating the outbound metadata frame 122 . In this way, deduplication flags can be used to prevent "duplication" of metadata blocks 140 of a particular type while still ensuring that at least one metadata block 140 of that particular type is included.

Figure 3b shows an example case where the deduplication flag is not set. In this case, transcoder 103 may be configured to consider block 140 of multiple inbound metadata frames 112 and 312 for creating outbound metadata frame 122 . Specifically, the transcoder 103 may be configured to: if the deduplication flag is not set (even where the outbound metadata frame 122 is generated from multiple inbound metadata frames 112, 312), then the Blocks 140 of data frame 312 are inserted into outbound metadata frame 122 .

A metadata block 140 inserted into a plurality of consecutive metadata frames 112, 312 (eg, inserted into each metadata frame 112, 312 of the bitstream 110) may be identified, for example, using a deduplication mark. In this way, the deduplication mark enables the transcoder 103 to easily identify metadata chunks 140 that can be discarded (without having to analyze the metadata stored in the data field 143 of the metadata chunk 140). Therefore, the computational complexity of transcoding metadata is reduced. On the other hand, an unset deduplication flag indicates that the corresponding metadata block 140 should not be discarded. This can be used for ancillary data to ensure that even if multiple inbound metadata frames 112, 312 are transcoded into a single outbound metadata frame 122, the ancillary data is not discarded.

Figures 4a and 4b illustrate an example use of a copy flag represented in descriptor 142 of metadata block 140. In the scenario shown, inbound content frame 111 includes a higher number of samples (ie, has a larger frame size) than outbound content frame 121 . If the frame sizes are different, it may happen that a sample of a single inbound content frame 111 is included in more than one outbound content frame 121, 321. Therefore, the transcoder 103 receives a single inbound metadata frame 112 and must determine in which of a plurality of outbound metadata frames 122, 322 to place a particular block of metadata 140. A copy flag may be used to indicate to the transcoder 130 whether a particular block 140 from the inbound metadata frame 112 is to be copied. As shown in Figure 4a, by setting the copy flag, it can be indicated that the metadata included in block 140 should be included in each outbound metadata frame 122, 322. On the other hand, an unset replication flag indicates that the metadata block 140 should be transferred only once. In this way, the transcoder 103 inserts the block 140 from the inbound metadata frame 112 into only a single outbound metadata frame of the plurality of outbound metadata frames 122, 322 (as shown in Figure 4b).

As mentioned above, descriptor 142 of metadata block 140 may represent an association tag (referred to as the "now_or_never" tag in Table 2). The association flag may indicate that the metadata included in block 140 may be delayed without affecting the content included in the associated content frame. Thus, if delaying metadata by an arbitrary amount of time is a property of the metadata, the syntax of the descriptor 142 may enable the transcoder 103 to delay the metadata by an arbitrary amount of time. This can be indicated by setting the flag now_or_never to 0. The association flag enables the transcoder 103 to transmit the metadata included in block 140, for example when the underlying audio codec can "afford" the transmission of the metadata, for example when the content frame includes silence. One example of metadata that may be delayed is ancillary data or binary data that does not need to be transmitted along with a specific content frame 121, such as a firmware upgrade.

As described in the context of Table 2, the descriptor 142 of the metadata block 140 may represent or may include a priority attribute or priority parameter. The priority parameter may represent the relative importance of metadata for a particular block 140 (eg, relative to the importance of other blocks 140). Transcoder 103 may determine to transcode only a certain number of metadata chunks 140 and discard all other metadata chunks in metadata frame 112 . This may be required, for example, when transcoding from a higher bitrate inbound bitstream 110 to a lower bitrate outbound bitstream 120. The priority parameter may enable the transcoder 103 to select those chunks 140 of the inbound metadata frame 112 that have a relatively highest priority and to discard (or delay) those chunks 140 that have a relatively lower priority.

The application and/or encoder 101 may provide multiple sets of metadata in the same metadata frame 112, each set of metadata having a different priority. Multiple sets of metadata can be associated with different qualities of metadata. Higher quality metadata can have a lower priority than lower quality metadata. In this way, the transcoder 103 may be configured to reduce the quality of metadata by taking into account priority parameters. As an example, if the priorities are set in such a way that scalability is possible, i.e. each set of metadata can be applied if all sets of metadata of higher priority for the same application are transmitted, then transcoding The processor can moderately degrade the quality of metadata without knowing the meaning of the metadata. Specifically, multiple sets of metadata may include incremental metadata, ie, each set of metadata may add some quality to the set of metadata with the next highest priority. The highest quality metadata can then be provided by combining all group metadata from highest priority down to lowest priority. As such, the inbound metadata frame 112 may include a plurality of incremental metadata chunks 140 , where the metadata chunk 140 with the highest priority includes a version of the metadata with the smallest acceptable quality, and where the metadata chunk 140 with successively lower priority Blocks 140 of levels include incremental versions of metadata that enable incremental improvements in the quality of the metadata. In this way, the transcoder 103 may determine the quality of the metadata included in the second bitstream 120 by considering the priority parameters of the plurality of blocks 140 of incremental metadata.

As shown in the example syntax of metadata frame 112 shown in Table 1, metadata frame 130 may include a protection field. The protection field may be used to enable the decoder 104 to verify whether the contents of the metadata frame 130 and/or the contents of the associated content frame have been modified and may therefore be invalid. In other words, the protection field may enable the decoder 104 to verify whether the metadata included in the metadata frame 130 and/or the associated content frame is trustworthy. Table 4 shows an example syntax for the protection field of metadata frame 130. The protection field may be included in the header 131 of the metadata frame 130.

Table 4

The semantics of protected fields can be as follows:

• protection_bits_frame may include the truncation protection payload of the current frame (including the content frame and/or associated metadata frame).

• protection_bits_history may include a truncation protection payload for the current frame and a truncation protection payload for frames preceding the current frame (including content frames and/or associated metadata frames). An example scheme for making frame sequences secure is described in WO2011/015369, the content of which is incorporated herein by reference.

As such, the protection field may include one or more encrypted values. An encrypted value may be generated based on metadata included in the current metadata frame (including protection fields) and/or based on the content frame associated with the current metadata frame. This way, it is guaranteed that isolated metadata frames and/or associated content frames are not modified. Another encrypted value may be generated based on metadata included in the current metadata frame and one or more previous metadata frames (and based on corresponding associated content frames). In this way, it is ensured that the sequence of content frames and/or the sequence of metadata frames are not modified.

The encryption value may be determined at the encoder 101 by applying a one-way function to a set of one or more metadata frames 112, 312 and/or associated content frames 111, 311. In particular, a secret key value and a cryptographic hash function (so-called one-way function) can be used to generate the encrypted value. Specifically, the HMAC-MD5 (Hash Message Authentication Code) of the data included in one or more metadata frames 112, 312 and the data included in one or more associated content frames 111, 311 can be calculated. ) value generates an encrypted value. Additionally, generation of the encrypted value may include truncation of the HMAC-MD5 value, for example, to 16, 24, 32, 48, 64, or 128 bits. Truncation may be beneficial in reducing the overhead required to encrypt values in the encoded bitstream 110 including the metadata frames 112, 312. It should be noted that other hash functions such as SHA-1 or SHA-256 can be used instead of MD5. Furthermore, it should be noted that the encoder 101 may be configured to send an encrypted value of 0 bits, ie, no encrypted value is sent, for example where metadata protection is not required.

In more detail, the encrypted value of one or more content frames 111, 311 and one or more The encrypted value of each metadata frame 112, 312. The "secret" key K is typically padded on the right with additional zeros to the block size of the hash function H(.) to determine one or more content frames 111, 311 and one or more metadata frames Hash Message Authentication Code (HMAC) of 112, 312. Let the || symbol represent concatenation, let the ⊕ symbol represent exclusive OR, and let the outer padding opad=0x5c5c5c...5c5c and the inner padding ipad=0x363636...3636 be constants for the length of the block size of the hash function H(.) , then the HMAC values of one or more content frames 111, 311 and one or more metadata frames 112, 312 can be written as

Where, m is a combined bit sequence of one or more content frames 111, 311 and one or more metadata frames 112, 312. The block size used by MD5 or SHA-1 or SHA-256 hash functions is usually 512 bits. The size of the output of the HMAC operation is the same as the size of the underlying hash function, i.e. 128 bits in the case of MD5 or 160 bits in the case of SHA-1.

In this way, the protected field can include at least two encrypted values

● Frame encryption value (referred to as "protection_bits_frame" in Table 4) that represents the reliability of each content frame 111 and its associated metadata frame 112. The frame encryption value can be used to identify whether the data of each content frame 111 and its associated metadata frame 112 have been changed. Frame encryption may be determined using a message m that includes the bit order of each content frame 111 and its associated metadata frame 112 (or the bit sequence of the payload included in each content frame 111 and its associated metadata frame 112 ). value.

• A historical encryption value (called "protection_bits_history" in Table 4) that represents the reliability of the sequence of at least two content frames 111, 311 and their associated at least two metadata frames 112, 312. The historical encryption value may be used to identify whether the sequence of at least two content frames 111, 311 and their associated metadata frames 112, 312 has been changed. A frame including at least two content frames 111, 311 and their associated at least two metadata frames 112, 312 (or at least two content frames 111, 311 and their associated at least two metadata frames 112, 312) may be used. m including the bit sequence of the payload) to determine the historical encryption value.

As mentioned above, the encryption value is determined using a security key K, which is generally known only to the encoder 101 and the decoder 104. In this document, it is proposed to achieve multi-level trust by allowing the use of different security keys K providing different levels of trust. As an example, at least two levels of trusted keys can be provided

● The high security key K ₁ may not be disclosed to any party other _than the entity providing components 101, 103, 104 along the distribution chain 100. Such an entity may be the provider of the codec system used along the distribution chain 100 (eg, Dolby Laboratories). In particular, such entities may be providers of encoders and decoders used along the distribution chain 100 . By keeping the high security key from being disclosed, it is ensured that the decoder 104 rendering the audio signal included in the received bitstream 120 can be confident that the metadata included in the metadata frames 122, 322 of the received bitstream 120 is authentic. and has not been modified in an unauthorized manner along the distribution chain 100.

• A medium security key K ₂ that may be disclosed to other parties such as parties operating along some of the components 101 , 103 , 104 of the distribution chain 100 (eg licensees of the provider of the codec system) Secret key K ₂ . If the decoder 104 receives a bitstream 120 that has been protected using a medium security key _K2 , the decoder 104 knows that the bitstream 120 includes metadata (in metadata frames 122, 322) that is Metadata that has been processed according to some policy of the operator of the distribution chain 100 which may be different from the policy of the provider of the codec system (who holds the high security key K ₁ ).

A representation of the security key K used by the encoder 101 may be provided in the metadata frame 130 (eg, in the header 131 of the metadata frame 130). The above situation is shown in Table 1 showing the key_id parameter. As shown in Table 4, the key_id parameter may include an index of a predetermined number of security keys, thereby enabling the decoder 104 to determine the security key K, which is used to determine one or more encrypted values, where one One or more encrypted values may be included in the protection() field of metadata frame 130. The decoder 104 may then use the identified security key to determine one or more encrypted values in the same manner as the corresponding encoder 101 performs. The encrypted value determined by decoder 104 may be referred to as the verified encrypted value. The verification encrypted value is then compared to the encrypted value stored in the metadata frame 103. In the case of a match, it is confirmed that the individual frames and/or sequence of frames have not been modified. On the other hand, in the case of a mismatch, it is confirmed that the individual frames and/or the sequence of frames have been modified.

Alternatively or in addition to providing a representation of the security key in the metadata frame 130, the decoder 104 may be configured to determine a plurality of sets of verification encryption values using a plurality of predetermined security keys known to the decoder 104. If one of the plurality of sets of verified encrypted values matches an encrypted value included in the metadata frame 130, the decoder 104 knows which security key has been used and that the respective frame and/or sequence of frames has not modified. On the other hand, non-matching of all sets of verified encryption values indicates that the individual frames and/or the sequence of frames have been modified.

Being able to detect which key was used to secure the bitstreams 110, 120 in the decoder 104 and transcoder 103 enables applications to make more fine-grained decisions about what to do with data of varying degrees of confidence. The decision may vary depending on the security key detected. Specifically, a high security key may be detected, a medium security key may be detected, or a valid key may not be detected and the security check fails.

In this way, when using multiple different security keys (attached to different trust levels), it is possible to provide individual level of credibility.

As described in the context of FIG. 1 , a distribution chain 100 for audio content may include a transcoder 103 configured to convert an inbound bitstream 110 into an outbound bitstream 120 . The transcoding performed by the transcoder 103 may relate to transcoding from a first audio codec system to a second, possibly different, audio codec system. Alternatively or additionally, the transcoding may be related to changes in the bitrate of the outbound bitstream 120 relative to the bitrate of the inbound bitstream 110 . The transcoder 103 may include a decoder for decoding the inbound bit stream 110 into a PCM (Pulse Code Modulation) audio signal. Additionally, the transcoder 103 may include an encoder for encoding the PCM audio signal into an outbound bitstream 120 . Such a transcoder 103 may be referred to as a "PCM connected" transcoder since one or more decoders (used to decode one or more inbound bitstreams 110) are connected via linear PCM to one or more More encoders (for encoding one or more outbound bitstreams 120).

The transcoder 103 may be a so-called professional transcoder, which is a device used by professional content providers such as broadcasters. As described above, the transcoder 103 may be configured to accept the inbound bitstream 110 in a first format (e.g., Dolby E) and transcode the inbound bitstream 110 to a different format (e.g., Dolby Digital +). Such a transcoder 103 typically includes one or more decoders (for decoding the inbound bitstream 110) and one or more encoders (for encoding the outbound bitstream 120).

A PCM connected transcoder may have one or more PCM processing stages between the decoder and encoder. Loudness leveling is an example of such PCM processing. Other examples of PCM processing include sample rate conversion, channel downmixing, and/or channel upmixing.

Such a PCM connected transcoder 103 raises challenges regarding the reliability, protection and trust issues mentioned above. As described above, the inbound bitstream 110 may include metadata frames 112, 112, 112, 110, 110, 110, 110, 110, 100, 100, 100, 100, 100, 100, 100, etc., protected using one or more encryption values (as shown in Tables 1 and 4, included in, for example, the protection fields of the metadata frames 112, 312). 312. The PCM connection transcoder 103 enables a user to make modifications to the PCM data obtained from the content frames 111, 311, thereby potentially invalidating the metadata included in the associated metadata frames 112, 312, and thus possibly compromising the availability of the metadata. reliability.

In this document, methods and systems for ensuring the trustworthiness of metadata in the transcoder 103 are described. In particular, the described method and system enable the authenticity of the metadata included in the metadata frames 112, 312 to be maintained even when the transcoder 103 is connected using PCM.

Figures 5a to 5d illustrate example PCM connection transcoders 503, 513, 523, 533 respectively. The transcoder includes a decoder 504 configured to convert the inbound bitstream 110 (which includes a sequence of content frames 111 and an associated sequence of metadata frames 112) into PCM data and metadata respectively. Decoder 504 may be configured to verify the correctness of inbound bitstream 110 using the protection scheme described above. For this purpose, the decoder 504 may be aware of some or all predetermined security keys.

Typically, the decoder 504 provides an unprotected set of PCM data and metadata (eg, on a frame-by-frame basis). In other words, the decoder 504 typically decodes each content frame 111 and associated metadata frame 112 and provides a corresponding set of PCM data and metadata without protection. In this manner, the decoder 504 provides sequences of sets of PCM data and metadata from corresponding sequences of content frames 111 and metadata frames 112 . The sequence of sets of PCM data and metadata may be modified by the transcoder and may then be passed to an encoder 501 configured to convert the (possibly modified) sequence of sets of PCM data and metadata into outbound bitstream 120. In this context, the encoder 501 generally cannot verify whether the sequence of (possibly modified) sets of PCM data and metadata has been modified in a perceptible manner. In other words, the encoder 501 may not be able to verify the plausibility of the (possibly modified) sequences of sets of PCM data and metadata.

In this document, it is proposed to enable the decoder 504 to provide one or more signature values based on one or more sets of PCM data and metadata, thereby enabling the protection of the PCM connection between the decoder 504 and the encoder 501 . As mentioned above, the signature value can be determined in a similar manner to the encrypted value. However, the signature value may also use a message m that includes one or more sets of PCM data and metadata (in contrast to one or more content frames and associated metadata frames). Specifically, decoder 504 may be configured to

● Determine frame signature values based on each set of PCM data and associated metadata; and

● Determine historical signature values based on two or more consecutive sets of PCM data and associated metadata.

In other words, within the PCM domain of the PCM connection transcoder 503 (i.e., between the decoder 504 and the encoder 501), one or more signatures (also called signature values) can be used to "protect" the credibility of the content . Decoder 504 may be configured to produce one or more signature values as output. When one or more signature values are generated by the decoder 504, one or more signature values may be calculated based on the union of the PCM data and regular metadata (obtained from the content frame) with additional metadata (obtained from the associated metadata frame). Multiple signature values. In this manner, for each frame of the inbound bitstream 110, one or more signature values may be determined based on the decoded sets of PCM data and metadata. The corresponding encoder 501 may use these one or more signature values to verify whether the received set of PCM data and metadata has been modified and/or is trustworthy.

Encoder 501 accepts as input one or more signature values along with PCM data, regular metadata and additional metadata. Encoder 501 may then check the signature value against other inputs (ie, against the received set or sets of PCM data and metadata). If other inputs have been modified/tampered with, the signature check will fail and the encoder will take appropriate action. Verification of one or more signature values may be performed at encoder 501 by determining based on one or more sets of PCM data and metadata received (in a manner similar to that described for encrypted values) Verify signature value.

In this way, the credibility of the decoded PCM data (and associated metadata) can be maintained in the PCM connection transcoder 503 by enabling the decoder 504 to base the decoded PCM data and associated metadata on One or more signature values are determined, and the corresponding encoder 501 is enabled to verify the authenticity of the PCM data (and associated metadata) to be encoded based on the one or more signature values. As mentioned above, the determination of one or more signature values and their verification can be performed based on a single or based on multiple leveled security keys K ₁ and K ₂ , wherein the one or more security keys can only Known to the decoder 504 and the encoder 501 and generally unknown to the entity performing PCM processing on the connection between the decoder 504 and the encoder 501 .

As shown in Figures 5a-5d, the use of one or more signature values enables various usage scenarios. Figure 5a shows a transcoder 503 where no PCM processing is performed between the decoder 504 and the encoder 503. Therefore, the protected data 510 (including one or more sets of PCM data and associated metadata and one or more associated signatures) is not modified and the chain of trust is maintained in the transcoder 503 . Accordingly, the transcoder 503 of Figure 5a is configured to receive an inbound bitstream comprising a sequence of protected and trusted inbound content frames 111 and associated inbound metadata frames 112 (also referred to as evolved frames) 110, and provides an outbound bitstream 120 that includes a sequence of protected and trusted outbound content frames 121 and associated outbound metadata frames 122. This is ensured by using one or more signatures to protect decoded PCM data, regular metadata and additional metadata (also called evolved metadata). Encoder 501 verifies one or more signatures and transmits additional metadata to outbound bitstream 120 as outbound metadata frames 122 . The use case shown in Figure 5a may for example be suitable for transcoding a bitstream from a first bitrate to a second bitrate.

Figure 5b shows a PCM connection transcoder 513 where the chain of trust is broken by an untrusted PCM processing stage 505. The PCM processing stage 505 receives the protected data 510 and modifies the data 510 . The PCM processing stage 505 is "untrusted" because the PCM processing stage 505 does not know the security key K used by the decoder 504. Thus, modified data 511 includes one or more sets of modified PCM data and associated metadata and one or more invalid signatures. Encoder 501 is configured to determine the invalidity of a signature and may be configured to take appropriate action. Specifically, encoder 501 may be configured to discard additional metadata from inbound metadata frames 112 , thereby providing an outbound bitstream 120 that includes only the sequence of content frames 121 but not the associated metadata frames 122 . By doing this, it is ensured that the transcoder 513 does not forward untrusted additional metadata. Furthermore, due to the fact that the bitstream 120 does not include the metadata frame 122, the bitstream 120 does not include the aforementioned encrypted value (from the protection field of the metadata frame 122). In this manner, decoder 104 may identify bitstream 120 as untrusted.

As described above, the encoder 501 may be configured to discard additional metadata from the inbound metadata frame 112 if one or more signature values are invalid. As described in the context of Table 2, the metadata chunks 140 of the inbound metadata frame 112 may represent corresponding descriptors 142 that describe one or more attributes of the corresponding metadata chunk 140. One of these attributes may be a PCM processing parameter (called tight_coupling parameter in Table 2). Encoder 501 may be configured to use the PCM processing parameters of metadata block 142 to determine whether the metadata included in metadata block 142 is to be included in outbound bitstream 120 . Specifically, the PCM processing parameters may indicate to the encoder 501 that the metadata from the block 140 of the inbound metadata frame 112 is still included in the outbound bitstream 120 even if the PCM samples of the associated content frame 111 have been modified. .

Table 5 shows example semantics of the PCM processing parameters (ie, the tight_coupling parameter of Table 2). In the example shown, a value of "0" for the PCM processing parameter indicates that the metadata block 140 should only be processed when no PCM processing occurs, for example only when one or more signature values have been verified by the encoder 501 The payload 143 (i.e. metadata) is included in the outbound bitstream 120. On the other hand, a value of "3" for the PCM processing parameter may mean that the payload 143 of block 140 should always be included on the outbound even if the PCM sample has been modified, e.g. even if one or more signature values have not been verified. Bitstream 120. Furthermore, the PCM processing parameters may have values representing intermediate cases, i.e., the PCM processing parameters may have values representing PCM processing conditions that need to be satisfied for the payload 143 to be included in the outbound bitstream 120 or to indicate that the payload 143 is not included in the outbound bitstream 120 . The value of the PCM processing condition in the case of outbound bitstream 120.

The PCM processing stage 505 may be configured to inform the encoder 501 about the processing that has been performed on the PCM samples in the PCM processing stage 505 . In other words, the PCM processing stage 505 may be configured to: notify the encoder 501 of PCM processing conditions (e.g., conversion of sample rates of PCM samples, inclusion of system sounds in PCM samples, modification of metadata, modification of channel configurations (e.g., Modify the mono signal into a stereo signal, or mix the 5.1 multi-channel signal into a stereo signal), adjust the loudness, etc.). In this manner, encoder 501 may be configured to receive a representation of PCM processing conditions from PCM processing stage 505 . Furthermore, the encoder 501 may be configured to process the metadata of the metadata block 140 based on the received PCM processing conditions and based on the values of the PCM processing parameters (eg, according to the semantics of Table 5).

table 5

Figure 5c shows the case of a PCM connection transcoder 523 configured to perform trusted PCM processing. This can be achieved by combining the PCM processing stage 506 with an additional re-signing stage 507. For this purpose, the trusted party may be provided with one or more security keys, thereby enabling the trusted party to re-sign the modified data 511. As an example, the trusted party may be provided with a medium security key _K2 . Accordingly, the modified data 511 may be re-signed (i.e., one or more signature values may be determined based on the modified data 511 using the medium security key _K2 ), thereby providing protected modified data 512 (including multiple A sequence of modified PCM data and associated metadata and one or more new signatures). Encoder 501 may be configured to verify the new signature and generate a trusted outbound bitstream 120 that includes a sequence of content frames 121 and a sequence of associated metadata frames 122 . Additionally, the encoder 501 may be configured to determine that the chain of trust has been broken and a new chain has been created because the re-signing stage 507 may have been used with the decoder 504 (which may have used the high security key K ₁ ) different security keys (eg, medium security key K ₂ ).

Figure 5d shows a block diagram of a PCM connected transcoder 533 including a PCM processing stage 509 in the encoder 501. Specifically, transcoder 533 is configured to maintain the chain of trust by ensuring that the PCM process is performed by an entity (eg, encoder 501 ) that knows the security key used by decoder 504 to determine one or more signature values. Encoder 501 is configured to verify one or more signatures protecting data 510 . The internal PCM processing stage 508 may then modify the received sets of PCM data and associated metadata. Furthermore, the encoder 501 may include a metadata update unit 509 configured to update metadata frames subject to modifications performed in the PCM processing stage 508 . Specifically, the metadata update unit 509 may be configured to determine an updated encryption value based on the transcoded content frame 121 and the metadata frame 122 . The updated encrypted value may then be included in the metadata frame 122 for communication to the decoder 104 .

Figure 6 provides another representation of transcoders 503, 513, 523 and 533 respectively.

In this document, methods and systems for transcoding metadata have been described. These methods and systems enable metadata to be transcoded with reduced computational complexity. Specifically, it is proposed to provide a descriptor for a metadata block, thereby enabling a transcoder to transcode metadata based solely on the descriptor, without the need to analyze the actual metadata included in the metadata block. By doing this, the complexity of the transcoder can be significantly reduced. Furthermore, this document provides methods and systems for protecting metadata frames and for protecting PCM data in PCM connected transcoders. Thus, it is ensured that the receiver of the transcoder metadata is provided with an indication of the trustworthiness of the received metadata.

The methods and systems described in this document may be implemented as software, firmware and/or hardware. Certain components may, for example, be implemented as software running on a digital signal processor or microprocessor. Other components may, for example, be implemented as hardware and/or as application specific integrated circuits. Signals encountered in the described methods and systems may be stored on a medium such as random access memory or optical storage media. Signals encountered in the described methods and systems may be transmitted via a network such as a radio frequency network, a satellite network, a wireless network, or a wired network such as the Internet. Typical devices using the methods and systems described in this document include portable electronic devices or other consumer devices for storing and/or rendering audio signals.

This technology can also be configured as follows.

(1) A transcoder (103) configured to: transcode an inbound bitstream (110) including an inbound content frame (111) and an associated inbound metadata frame (112) to include an outbound an outbound bitstream (120) of an inbound content frame (121) and an associated outbound metadata frame (122); wherein said inbound content frame (111) represents a signal encoded in accordance with a first codec system, and wherein said outbound content frame (121) represents a signal encoded according to a second codec system; wherein said transcoder (103) is configured to:

- identifying a metadata inbound block (140) from said inbound metadata frame (112); wherein said metadata inbound block (140) is identical to a associated with the inbound descriptor (142) of one or more attributes of the metadata; and

- Generate the outbound metadata frame (122) from the inbound metadata frame based on the inbound descriptor (142).

(2) The transcoder (103) according to (1), wherein the transcoder (103) is configured to generate the outbound metadata frame (122) by:

-Copy metadata from said inbound block (140) to the outbound block (140);

as well as

- inserting said outbound block (140) into said outbound metadata frame (122); wherein said copy and said insertion are subject to said one represented by said inbound descriptor (142) or more attributes.

(3) The transcoder (103) according to (2), wherein the transcoder (103) is configured to pass the inbound descriptor (142) based on the inbound block (140) ) generates an outbound descriptor (142) of the outbound block (140) to generate the outbound metadata frame (122).

(4) The transcoder (103) according to (3), wherein the transcoder (103) is configured to: Modifications are made to generate the outbound descriptor (142); wherein the outbound descriptor (142) represents the modified one or more attributes.

(5) The transcoder (103) according to any of the preceding, wherein the transcoder (103) is configured to: based solely on the one or and generating the outbound metadata frame (122) based on the inbound metadata frame (112).

(6) The transcoder (103) according to any one of the preceding, wherein the transcoder (103) is configured to: perform analysis without analyzing metadata included in the inbound block (140). In this case, the outbound metadata frame (122) is generated based on the inbound metadata frame (112).

(7) The transcoder (103) according to any of the preceding, wherein the one or more attributes include one or more of the following:

- a timestamp parameter representing a sample of said signal; wherein the metadata of said inbound block (140) is associated with the sample of said signal;

- a duration parameter representing a number of samples of said signal; wherein the metadata of said inbound block (140) is associated with said number of samples of said signal;

- a transcoding parameter indicating whether said inbound block (140) is to be transcoded into said outbound bitstream (120);

- a replication parameter indicating whether the metadata of said inbound block (140) is to be included in each outbound metadata frame (122, 322) generated from said inbound metadata frame (112);

- Deduplication parameter indicating whether the metadata of the inbound block (140) is to be transferred if the outbound metadata frame (122) is generated based on multiple inbound metadata frames (112, 312). Coder(103) discard;

- a priority parameter indicating the importance of the metadata of said inbound block (140) relative to one or more other inbound blocks of metadata (140);

- an association parameter indicating whether the metadata of the inbound block (140) can be inserted into a delayed outbound metadata frame (322) following the outbound metadata frame (112); and/or

- a PCM processing parameter indicating whether the metadata of the inbound block (140) is to be discarded by the transcoder (103) in case of modifications to the data included in the inbound content frame (111) .

(8) The transcoder (103) according to any of the preceding items, wherein

- said one or more attributes include a timestamp parameter (201) representing a sample (202) of said signal to which metadata of said inbound block (140) is associated wherein the timestamp parameter (201) of the inbound descriptor (142) represents a sample (202) of the signal associated with the inbound content frame (111);

- the transcoder (103) is configured to generate an outbound block (140) based on the inbound block (140); and

- said transcoder (103) is configured to generate an outbound descriptor (142) of said outbound block (140) by modifying said timestamp parameter (201) of said inbound descriptor (142) ), such that the timestamp parameter (203) of the outbound descriptor (142) represents a sample (202) of the signal associated with the outbound content frame (121).

(9) The transcoder (103) according to any of the preceding items, wherein

- the one or more attributes include a timestamp parameter (201) representing a sample (202) of the signal with which the metadata of the inbound block (140) is associated; wherein said timestamp parameter (201) of said inbound descriptor (142) represents a sample (202) of said signal associated with said inbound content frame (111);

- the transcoder (103) is configured to generate an outbound block (140) based on the inbound block (140);

- the transcoder (203) is configured to insert the outbound block (140) into a delayed outbound metadata frame (222);

- said delayed outbound metadata frame (222) is associated with a delayed outbound content frame (221) that does not include said sample (202) of said signal; and

- the transcoder (103) is configured to generate an outbound descriptor (142) of the outbound block (140) by modifying the timestamp parameter (201) of the inbound block (140) to causing the timestamp parameter (213) of the outbound descriptor (142) to represent a sample (202) of the signal associated with the delayed outbound content frame (221);

(10) The transcoder (103) according to any of the preceding items, wherein

- said one or more attributes include a replication parameter indicating whether the metadata of said inbound block (140) is to be included in each outbound block generated from said inbound metadata frame (112) in the station metadata frame (122, 322); and

- The transcoder (103) is configured to generate a plurality of outbound metadata frames (122, 322) from the inbound metadata frame (112) by taking into account the replication parameters.

(11) The transcoder (103) according to (10), wherein the transcoder (103) is configured to

- determining that said replication parameters represent metadata of said inbound block (140) to be included in each outbound metadata frame (122, 322) generated from said inbound metadata frame (112);

- Inserting the metadata of the inbound block (140) into each of the plurality of outbound metadata frames (122, 322).

(12) The transcoder (103) according to any of (10) to (11), wherein the replication parameters include a flag that can be set to represent the inbound block (140) of metadata to be included in each outbound metadata frame (122, 322) generated from the inbound metadata frame (112), or the flag can be set to represent the inbound block (140 ) metadata shall not be included in each outbound metadata frame (122, 322) generated from said inbound metadata frame (112).

(13) The transcoder (103) according to any one of (10) to (12), wherein

- the transcoder (103) is configured to generate a plurality of outbound content frames (121, 321) based on the inbound content frame (111); and

- the plurality of outbound content frames (121, 321) are associated with corresponding outbound metadata frames of the plurality of outbound metadata frames (122, 322).

(14) The transcoder (103) according to any of the preceding, wherein the one or more attributes include

- Deduplication parameter indicating whether the metadata of the inbound block (140) can be transferred if the outbound metadata frame (122) is generated based on multiple inbound metadata frames (112, 312). Coder(103) discard;

- the transcoder (103) is configured to generate said outbound metadata frame from a plurality of inbound metadata frames (112) of the inbound bitstream (110) by taking into account said deduplication parameters (122).

(15) The transcoder (103) according to (14), wherein

- said plurality of inbound metadata frames (112) comprise a plurality of inbound metadata blocks (140), each said inbound block (140) together with metadata representing said inbound block (140) may be Corresponding deduplication parameters discarded by the transcoder (103) are associated; and

- the transcoder (103) is configured to, for all but one inbound metadata frame of the plurality of inbound metadata frames (112, 312), discard said plurality of inbound metadata frames (112, 312). of inbound chunks (140) of metadata to generate the outbound metadata frame (122).

(16) The transcoder (103) according to any one of (14) to (15), wherein

- the transcoder (103) is configured to generate the outbound content frame (121) based on a plurality of inbound content frames (111, 311); and

- the plurality of inbound content frames (111, 311) are associated with corresponding inbound metadata frames of the plurality of inbound metadata frames (112, 312).

(17) The transcoder (103) according to any one of (14) to (16), wherein the de-duplication parameters include a flag that may be set to indicate that if metadata frame (112, 312) to generate the outbound metadata frame (122), then the metadata of the inbound block (140) can be discarded by the transcoder (103); or the mark can is set to indicate that if the outbound metadata frame (122) is generated from a plurality of inbound metadata frames (112, 312), the metadata of the inbound block (140) may not be transferred. Encoder (103) discarded.

(18) The transcoder (103) according to any of the preceding items, wherein

- the one or more attributes include a priority parameter representing the relative importance of the metadata of the inbound block (140) with respect to one or more other inbound blocks of metadata (140);

- the inbound metadata frame (112) includes a plurality of inbound blocks (140) with descriptors (142) representing different values of the priority parameter; and

- said transcoder (103) is configured to generate said outbound metadata based on said plurality of inbound blocks (140) according to said priority parameters of said plurality of inbound blocks (140) frame(122).

(19) The transcoder (103) according to (18), wherein

- said plurality of inbound blocks (140) are associated with an incremental priority parameter representing an incremental priority;

- the plurality of inbound blocks (140) include incremental metadata such that the combined metadata of the plurality of inbound blocks (140) provides high quality metadata and such that the combined metadata of the plurality of inbound blocks (140) Metadata for the inbound block (140) with the highest relative priority provides metadata of reduced quality; and

The transcoder (103) is configured to generate the outbound metadata frame (122) based on one or more of the plurality of inbound blocks (140) such that the outbound The quality of the metadata included in the station metadata frame (122) can be scalably degraded.

(20) The transcoder (103) according to any of the preceding items, wherein

- the one or more attributes include an association parameter indicating whether the metadata of the inbound block (140) can be inserted into a delayed outbound after the outbound metadata frame (112) In station metadata frame (222);

- The transcoder (103) is configured to insert metadata from the inbound chunk (140) into the in the outbound metadata frame (122).

(21) The transcoder (103) according to (20), wherein

- the transcoder is configured to insert metadata from the inbound block (140) into the In the delayed outbound metadata frame (222) following the outbound metadata frame (122).

(22) The transcoder (103) according to any of the preceding items, wherein

- the inbound metadata frame (112) and the outbound metadata frame (122) follow a common syntax;

- the common syntax enables a metadata frame (130) to include zero metadata blocks (140), one or more metadata blocks (140);

- Each metadata block (140) represents a corresponding descriptor (142) representing one or more attributes of the metadata included in the corresponding metadata block (140).

(23) The transcoder (103) according to any of the preceding items, further configured to

- generating said outbound content frame (121) from said inbound content frame (111) using a decoder of said first codec system and an encoder of said second codec system.

(24) The transcoder (103) according to any of the preceding items, wherein

- said signal includes an audio signal; and/or

- said inbound content frames (111) represent some or all samples of frames of said signal; and

- The outbound content frames (121) represent some or all samples of frames of the signal.

(25) The transcoder (103) according to any of the preceding items, wherein

- the first codec system is different from the second codec system; and/or

- said first codec system and said second codec system comprise one or more of the following: Dolby E, Dolby Digital Plus, Dolby Digital, Dolby TrueHD, Dolby Pulse, AAC and/or HE-AAC.

(26) The transcoder (103) according to any of the preceding, wherein the bitrate of the outbound bitstream (120) is different from the bitrate of the inbound bitstream (110).

(27) A method for transcoding an inbound bitstream (110) including an inbound content frame (111) and associated inbound metadata frame (112) to include an outbound content frame (121) and associated A method of outbound bitstream (120) of an outbound metadata frame (122); wherein said inbound content frame (111) represents a signal encoded according to a first codec system, and wherein said outbound The content frame (121) represents a signal encoded according to the second codec system; wherein the method includes:

- identifying a metadata inbound block (140) from said inbound metadata frame (112); wherein said metadata inbound block (140) is identical to a associated with the inbound descriptor (142) of one or more attributes of the metadata; and

- Generate said outbound metadata frame (122) from said inbound metadata frame (112) based on said inbound descriptor (142).

(28) An encoded bitstream (110) comprising a content frame (111) and an associated metadata frame (112); wherein the content frame (111) represents a signal encoded according to a first codec system; wherein the metadata frame (112) includes a metadata block (140); wherein the metadata block (140) is associated with one or more attributes representing metadata included in the metadata block (140) associated with the descriptor (142).

(29) An encoder (101) configured to generate an encoded bitstream (110) comprising a content frame (111) and an associated metadata frame (112); wherein the content frame (111) represents a A signal encoded by a first codec system; wherein the encoder (101) is configured to

-Generate metadata block(140);

- Determining a descriptor (142) associated with said metadata block (140); wherein said descriptor (142) represents one or more attributes of metadata included in said metadata block (140) ;as well as

- Inserting the metadata block (140) into the metadata frame (112).

(30) The encoder (101) according to (29), wherein

- said one or more attributes include a timestamp parameter (213) representing a sample (202) of said signal with which metadata of said block (140) is associated;

- the encoder (101) is configured to insert the block (140) into a delayed metadata frame (222);

- said delayed metadata frame (222) is associated with a delayed content frame (221) that does not include said sample (202) of said signal; and

- the encoder (101) is configured to generate the descriptor (142) of the block (140) such that the timestamp parameter (213) of the descriptor (142) represents the same as the delayed content frame ( 221) Samples (202) of said signal in question.

(31) A method for generating an encoded bitstream (110) comprising a content frame (111) and an associated metadata frame (112); wherein the content frame (111) represents a System coded signal; wherein the method includes

-Generate metadata block(140);

- Determining a descriptor (142) associated with said metadata block (140); wherein said descriptor (142) represents one or more of said metadata included in said metadata block (140) attributes; and

- Inserting the metadata block (140) into the metadata frame (112).

(32) An encoder (101) configured to generate an encoded bitstream (110) including a content frame (111) and an associated metadata frame (112); wherein the content frame (111) represents a A signal encoded by a first codec system; wherein the encoder (101) is configured to

-Generate metadata block(140);

- inserting the metadata block (140) into the metadata frame (112);

- selecting a security key from a plurality of predetermined security keys; wherein said plurality of predetermined security keys provide different levels of trust;

- generating an encrypted value based at least on the content frame (111), the associated metadata frame (112) and the selected security key; and

- Insert the generated encrypted value into the metadata frame (112).

(33) The encoder (101) according to (32), wherein the plurality of predetermined security keys include

- a highly secure key known only to the developer of said encoder (101); and

- A medium security key known to the operator of said encoder (101).

(34) The encoder (101) according to any one of (32) to (33), wherein the encoder (101) is configured to

- generate a plurality of consecutive content frames (111, 311) and associated metadata frames (112, 312) for said encoded bitstream (110);

- Generating a frame encryption value based on a single content frame (111) and its associated metadata frame (112) and based on the selected security key; and

- Generate historical encryption values based on at least some of the plurality of consecutive content frames (111, 311) and their associated metadata frames (112, 312) and based on the selected security value.

(35) The encoder (101) according to any one of (32) to (34), wherein the encoder (101) is configured to: calculate an HMAC-MD5 value or HMAC for generating an encrypted value -SHA256 value.

(36) The encoder (101) according to (35), wherein the encoder (101) is configured to truncate an HMAC-MD5 value or an HMAC-SHA256 value to produce the encrypted value.

(37) The encoder (101) according to any of (32) to (36), wherein the encoder (101) is configured to insert a representation of a selected security key into the element. in data frame (112).

(38) A method for generating an encoded bitstream (110) comprising a content frame (111) and an associated metadata frame (112); wherein the content frame (111) represents a System coded signal; wherein the method includes

-Generate metadata block(140);

- inserting the metadata block (140) into the metadata frame (112);

- selecting a security key from a plurality of predetermined security keys; wherein said plurality of predetermined security keys provide different levels of trust;

- generating an encrypted value based at least on the content frame (111), the associated metadata frame (112) and the selected security key; and

- Insert the generated encrypted value into the metadata frame (112).

(39) A transcoder (503) configured to transcode an inbound bitstream (110) including an inbound content frame (111) and an associated inbound metadata frame (112) into outbound bits stream (120); wherein the inbound bitstream (110) represents a set of samples of a signal; wherein the transcoder (103) includes

-Decoder (504), configured to

- converting said inbound content frame (111) into a set of decoded PCM samples of said signal;

- extract metadata from said inbound metadata frame (112); and

- generating a signature value using the decoder security key for the set of decoded PCM samples and the extracted metadata; and

-Encoder(501), configured to

-Receive a set of PCM samples and associated metadata;

-Receive signature value;

- Verify that the received signed value is valid for the received set of PCM samples and associated metadata using the encoder security key; and

- If the received signature is valid, generate an outbound content frame (121) of the outbound bitstream (120) based on the received set of PCM samples and generate the outbound bitstream based on the received metadata ( The associated outbound metadata frame (122) of 120).

(40) The transcoder (503) according to (39), wherein the encoder (501) is configured to use the decoder security key as the encoder security key.

(41) The transcoder (503) according to any of (39) to (40), wherein the encoder (501) is configured to prevent the received signature from being The received metadata is inserted into the outbound bitstream (120).

(42) The transcoder (503) according to any one of (39) to (41), further comprising a PCM processing stage (505, 506) configured to

- modifying said set of decoded PCM samples and/or extracted metadata to produce a second set of PCM samples and second metadata; and

-Transmitting said second set of PCM samples and said second metadata to said encoder (501).

(43) The transcoder (503) according to (42), further comprising a re-signing unit 507 configured to

- determining an updated signature value using a re-sign security key for said set of second PCM samples and said second metadata; and

-Transmit the updated signature value to the encoder (501).

(44) The transcoder (503) according to (43), wherein

- the re-signing security key is different from the decoder security key; and

- The encoder (501) is configured to use the re-sign security key as the encoder security key.

(45) The transcoder (503) according to any one of (39) to (44), wherein

- the encoder (501) includes a PCM processing stage (508) configured to modify a received set of PCM samples and/or received metadata; and

- The encoder (501) is configured to generate the outbound content frame (121) and/or the outbound content frame (121) based on the modified received set of PCM samples and/or the modified received metadata. Outbound metadata frame (122).

(46) The transcoder (503) according to any one of (39) to (45), wherein

- said decoder (504) is configured to identify a metadata inbound block (140) from said inbound metadata frame (112); wherein said metadata inbound block (140) is identical to said metadata inbound block (140) representing said metadata an inbound descriptor (142) associated with one or more attributes of the metadata included in the data inbound block (140); and

- The encoder (501) is configured to generate the outbound metadata frame (122) from the inbound metadata frame (112) based on the inbound descriptor (142).

(47) The transcoder (503) of (46), wherein the one or more attributes include PCM processing parameters that indicate when modifications to the set of PCM samples have been made. and/or whether the metadata of the inbound block (140) is to be discarded by the encoder (501) in the case of modifications to the extracted metadata.

(48) The transcoder (503) according to (47), wherein the encoder (501) is configured to: even if the set of PCM samples and/or the extracted metadata have been modified, if If the PCM processing parameter indicates that the metadata of the inbound block (140) should not be discarded, the metadata of the inbound block (140) is included in the outbound metadata frame (122).

(49) The transcoder (503) according to (47) forwardly dependent on any of (42) to (44), wherein

- the PCM processing stage (505) is configured to: provide a representation of one or more PCM processing conditions to the encoder (501);

- the one or more PCM processing conditions represent how the set of PCM samples and/or extracted metadata has been processed by the PCM processing stage (505); and

- the encoder is configured to generate the outbound metadata frame (122) from the inbound metadata frame (112) further based on the one or more PCM processing conditions.

(50) The transcoder (503) of (49), wherein the one or more PCM processing conditions include one or more of: conversion of the sampling rate of the set of PCM samples , the mixing of the PCM samples with the system sound, the modification of the extracted metadata, the modification of the channel configuration of the set of PCM samples, the leveling of the loudness of the set of PCM samples.

(51) A method for transcoding an inbound bitstream (110) including an inbound content frame (111) and associated inbound metadata frame (112) to an outbound bitstream (120); wherein , the inbound bitstream (110) represents a set of samples of the signal; the method includes,

At the decoder (504),

- converting said inbound content frame (111) into a set of decoded PCM samples of said signal;

- extract metadata from said inbound metadata frame (112); and

- generating a signature value using the decoder security key for the set of decoded PCM samples and the extracted metadata;

- transmitting the set of decoded PCM samples, extracted metadata and generated signature values to the corresponding encoder (501); and

At the encoder (501)

-Receive a set of PCM samples and associated metadata;

-Receive signature value;

- Use the encoder security key to determine whether the received signature value is valid for the received set of PCM samples and associated metadata; and

- If the received signature is valid, generate an outbound content frame (121) of the outbound bitstream (120) based on the received set of PCM samples and generate the outbound bitstream based on the received metadata ( The associated outbound metadata frame (122) of 120).

(52) A decoder (104) configured to receive an encoded bitstream (110) including a content frame (111) and an associated metadata frame (112); wherein the content frame (111) represents a A signal encoded by a first codec system; wherein the decoder (104) is configured to

- Extract encrypted values from said metadata frame (112);

- Determining a security key based on a plurality of predetermined security keys; wherein the plurality of predetermined security keys provide different levels of trust;

- generating a verification encrypted value based at least on said content frame (111), said associated metadata frame (112) and the determined security key; and

- Compare the extracted encrypted value with the verified encrypted value to determine whether the received encoded bitstream can be trusted (110).

(53) The decoder (104) of (52), wherein the decoder (104) is configured to determine the security key by extracting the security key from the metadata frame (112). Security key.

(54) The decoder (104) according to any one of (52) to (53), wherein the decoder (104) is further configured to determine which of the plurality of predetermined security keys Which security key has been used to generate the extracted encryption value to determine the trust level of the received encoded bitstream (110).

(55) The decoder (104) according to any one of (52) to (54), wherein the decoder (104) is configured to

- Generate multiple verification encryption values for the plurality of predetermined security keys respectively;

- comparing each of the plurality of verified encrypted values with the extracted encrypted value; and

- if one of the plurality of verified encrypted values matches the extracted encrypted value, determining that one of the plurality of predetermined security keys has been used to generate the extracted encrypted value .

(56) A method for determining a trust level of a received encoded bitstream (110) comprising a content frame (111) and an associated metadata frame (112); wherein the content frame (111) represents a a signal encoded by a first codec system; wherein the method includes

- Extract encrypted values from said metadata frame (112);

- Determining a security key based on a plurality of predetermined security keys; wherein the plurality of predetermined security keys provide different levels of trust;

- generating a verification encrypted value based at least on said content frame (111), said associated metadata frame (112) and the determined security key; and

- Comparing the extracted encrypted value with the verified encrypted value to determine whether the received encoded bitstream can be trusted based on the determined trust level of the security key (110).

(57) A decoder (504) configured to decode an inbound bitstream (110) including an inbound content frame (111) and an associated inbound metadata frame (112); wherein The inbound bitstream (110) represents a set of samples of a signal; wherein the decoder (504) is configured to

- converting said inbound content frame (111) into a set of decoded PCM samples of said signal;

- extract metadata from said inbound metadata frame (112);

- generating a signature value using the decoder security key for the set of decoded PCM samples and the extracted metadata; and

-Sending the set of decoded PCM samples, extracted metadata and generated signature values to the encoder (501) for re-encoding.

(58) An encoder (501) configured to encode an outbound bitstream (120) including an outbound content frame (121) and an associated outbound metadata frame (122), wherein The encoder (501) is configured to

-Receive a set of PCM samples and associated metadata;

- receiving signature values for said set of PCM samples and associated metadata;

- Verify that the received signed value is valid for the received set of PCM samples and associated metadata using the encoder security key; and

- If the received signature is valid, generate an outbound content frame (121) of the outbound bitstream (120) based on the received set of PCM samples and generate the outbound bitstream based on the received metadata ( The associated outbound metadata frame (122) of 120).

(59) A set of methods for decoding an inbound bitstream (110) including an inbound content frame (111) and an associated inbound metadata frame (112); wherein said inbound bitstream (112) 110) A set of samples representing a signal; wherein the method includes

- converting said inbound content frame (111) into a set of decoded PCM samples of said signal;

- extract metadata from said inbound metadata frame (112);

- using the decoder security key to generate a signature value for the set of decoded PCM samples and extracted metadata; and

- Providing the set of decoded PCM samples, extracted metadata and generated signature values to the encoder (501) for re-encoding.

(60) A method for encoding an outbound bitstream (120) including an outbound content frame (121) and an associated outbound metadata frame (122); wherein the method includes

-Receive a set of PCM samples and associated metadata;

- receiving signature values for said set of PCM samples and associated metadata;

- Verify that the received signed value is valid for the received set of PCM samples and associated metadata using the encoder security key; and

- If the received signature is valid, generate an outbound content frame (121) of the outbound bitstream (120) based on the received set of PCM samples and generate the outbound bitstream based on the received metadata ( The associated outbound metadata frame (122) of 120).

(61) A decoder (104) configured to decode an encoded bitstream (110) including a content frame (111) and an associated metadata frame (112); wherein the content frame (111 ) represents a signal encoded according to a first codec system; wherein said metadata frame (112) includes a metadata block (140); wherein said metadata block (140) and represents said metadata block (140 ); wherein the decoder (104) is configured to

- decoding the encoded signal included in said content frame (111);

- identifying said metadata block (140) from said metadata frame (112);

-Extract the descriptor (142) from the metadata block (140); and

- Processing the metadata included in the metadata block (140) according to the one or more attributes represented by the descriptor (142).

(62) A method for decoding an encoded bitstream (110) comprising a content frame (111) and an associated metadata frame (112); wherein the content frame (111) represents a A signal encoded by a decoder system; wherein the metadata frame (112) includes a metadata block (140); wherein the metadata block (140) and represents metadata included in the metadata block (140) associated with a descriptor (142) of one or more attributes; wherein the method includes

- decoding the encoded signal included in said content frame (111);

- identifying said metadata block (140) from said metadata frame (112);

- extracting said descriptor (142) from said metadata block (140); and extracting said descriptor (142) from said metadata block (140) based on said one or more attributes represented by said descriptor (142) Included metadata is processed.

Claims (14)

1. A method of encoding, comprising:

encoding a current content frame;

generating a protection field for an associated metadata frame, the associated metadata frame being associated with the current content frame;

Encoding the associated metadata frame, the associated metadata frame including the protection field; and

including the encoded current content frame and the encoded associated metadata frame in an output bitstream, wherein:

generating the protection field involves generating one or more encrypted values;

at least one of the one or more encryption values is a frame encryption value representing an authenticity of the encoded current content frame; and

the frame encryption value is generated by applying a one-way function to a set of frames including the encoded current content frame and the encoded associated metadata frame.

2. The encoding method of claim 1, wherein at least one of the one or more encryption values is generated by applying a one-way function to a set of frames including a preceding encoded content frame and an encoded metadata frame associated with the preceding encoded content frame.

3. The encoding method of claim 2, wherein the protection field includes a historical encryption value representing authenticity of at least two encoded content frames and at least two encoded metadata frames.

4. The encoding method of claim 1, wherein at least one of the one or more encrypted values is generated using a key value and a cryptographic hash function.

5. The encoding method of claim 4, wherein:

the key value corresponds to a security key selected from a plurality of predetermined security keys;

a first key of the plurality of predetermined security keys corresponds to a first trust level; and

a second key of the plurality of predetermined security keys corresponds to a second trust level, the second trust level being different from the first trust level.

6. The encoding method of claim 5, wherein:

the first key is a highly secure key; and

the second key is a medium security key.

7. An encoding apparatus comprising one or more hardware elements, the encoding apparatus configured to:

encoding a current content frame;

generating a protection field for an associated metadata frame, the associated metadata frame being associated with the current content frame;

encoding the associated metadata frame, the associated metadata frame including the protection field; and

including the encoded current content frame and the encoded associated metadata frame in an output bitstream, wherein:

Generating the protection field involves generating one or more encrypted values;

at least one of the one or more encryption values is a frame encryption value representing an authenticity of the encoded current content frame; and

the frame encryption value is generated by applying a one-way function to a set of frames including the encoded current content frame and the encoded associated metadata frame.

8. The encoding device of claim 7, wherein at least one of the one or more encryption values is generated by applying a one-way function to a set of frames including a previous encoded content frame and an encoded metadata frame associated with the previous encoded content frame.

9. The encoding apparatus of claim 8, wherein the protection field comprises a historical encryption value representing authenticity of at least two encoded content frames and at least two encoded metadata frames.

10. The encoding apparatus of claim 7, wherein at least one of the one or more cryptographic values is generated using a key value and a cryptographic hash function.

11. One or more non-transitory media storing software comprising instructions for performing an encoding method comprising:

Encoding a current content frame;

generating a protection field for an associated metadata frame, the associated metadata frame being associated with the current content frame;

encoding the associated metadata frame, the associated metadata frame including the protection field; and

including the encoded current content frame and the encoded associated metadata frame in an output bitstream, wherein:

generating the protection field involves generating one or more encrypted values;

at least one of the one or more encryption values is a frame encryption value representing an authenticity of the encoded current content frame; and

the frame encryption value is generated by applying a one-way function to a set of frames including the encoded current content frame and the encoded associated metadata frame.

12. The one or more non-transitory media of claim 11, wherein at least one of the one or more encryption values is generated by applying a one-way function to a set of frames including a prior encoded content frame and an encoded metadata frame associated with the prior encoded content frame.

13. The one or more non-transitory media of claim 12, wherein the protection field includes a historical encryption value representing authenticity of at least two encoded content frames and at least two encoded metadata frames.

14. The one or more non-transitory media of claim 11, wherein at least one of the one or more encrypted values is generated using a key value and a cryptographic hash function.